Net Promoter Score (NPS): Meaning, Scale & How to Calculate

Net Promoter Score (NPS) is a customer-loyalty metric, measured on a 0–10 scale, that captures how likely customers are to recommend you. It’s calculated as the percentage of Promoters minus the percentage of Detractors, producing a single number from −100 to +100.

What is Net Promoter Score (NPS)?

Net Promoter Score (NPS) is a customer loyalty metric that shows how likely your customers are to recommend your business to others.
Simply put, it’s like a customer satisfaction scorecard that can predict your business growth based on word-of-mouth advocacy.

Who Created NPS?

Fred Reichheld introduced NPS in 2003, and since then, it has become widely recognized as the go-to method for measuring customer experience.
Its popularity stems from being both simple and effective.

This metric converts complex customer satisfaction data into a clear, actionable number.
Businesses can use this number to understand and enhance their customer relationships.

What Can You Measure Using NPS?

Net Promoter Score (NPS) reveals customer satisfaction from many angles, giving your business a detailed understanding of where you’re winning and where you can improve.

Many large companies use NPS as a company-wide health check, a quick read on how customers feel about the business as a whole. But that’s just the starting point.

Product-Level Insights

You can zoom in to see how specific products are doing. A company with several products can run a separate NPS survey for each one and see which products customers would recommend and which they would not.

Feature-Level Feedback

Want to get even more specific? Ask about individual features, for example right after a customer uses a new feature for the first time. This tells you what to improve next.

Customer Journey Mapping

NPS also helps map the customer journey by measuring satisfaction at key moments like:

• Right after a purchase
• During customer service conversations
• While using the website
• When interacting with mobile apps

Segmented Customer Insights

Plus, you can slice and dice NPS data to understand different customer groups:

• • New customers versus loyal ones
  • Various subscription levels
  • Different regions
  • Business versus individual customers

This comprehensive view helps companies make smart decisions about where to focus their improvement efforts and investments.

How to Calculate Your Net Promoter Score (NPS)

Net Promoter Score (NPS) takes customer feedback and turns it into clear, usable numbers through a simple formula. Let’s break down how to define Net Promoter Score.

Step 1: Ask Your Customers

Start by asking your customers one key question: “How likely are you to recommend us?” They answer on a scale of 0-10. Based on their responses, customers fall into three groups:

Group	Score	Who they are
Promoters	9–10	Loyal enthusiasts who love your brand and refer others.
Passives	7–8	Satisfied but unenthusiastic; easily lured away by competitors.
Detractors	0–6	Unhappy customers likely to discourage others from using your services.

Step 2: Group Responses

Here’s an example with 200 customers:

• 100 people gave 9-10 ratings = 50% Promoters
• 60 people scored 7-8 = 30% Passives
• 40 people rated 0-6 = 20% Detractors

Step 3: Use the Formula

To calculate your NPS, subtract the percentage of Detractors from the percentage of Promoters:

NPS = % Promoters – % Detractors

In this example:

50% (Promoters) – 20% (Detractors) = an NPS of 30

Key Points to Remember

• Your NPS can range from -100 to +100.
• Passives are excluded from the final calculation.
• The result is a whole number, not a percentage.

Does the NPS Have to Be from 1 to 10? Why 0-10 is the Industry Standard

The Net Promoter Score (NPS) system specifically uses a 0-10 scale, not 1-10. This wasn’t a random choice, it was carefully designed by Fred Reichheld at Bain & Company and has become the global standard for measuring customer experience.

Why Zero Matters

Think of it like a temperature scale, having zero as your starting point matters. In NPS:

• 0: Represents complete unwillingness to recommend.
• 10: Shows the highest possible enthusiasm.

This 11-point range gives customers enough options to accurately reflect their feelings.

Alternative Scales and Their Limitations

While some companies might try different scales, like 1-5 stars or 1-7 ratings, these alternatives don’t provide the same insights as the standard NPS scale. Here’s why the 0-10 scale stands out:

Industry Consistency

• The 0-10 scale allows companies to compare their performance across different industries.
• Most NPS tools are built specifically for this range, ensuring reliable measurement.

Scale Integrity

• Using any other scale changes the fundamental NPS methodology.
• Other scales might measure satisfaction, but they don’t calculate true Net Promoter Scores.
• The 0-10 range is essential for properly categorizing customers as Promoters, Passives, or Detractors.

How to Calculate NPS in Excel

Net Promoter Score (NPS) can be calculated in Excel using a straightforward process. This guide will help you set up a template for efficiently calculating NPS based on customer responses.

Excel Template for NPS Calculation

Column Setup

• A1: “Response ID”
• B1: “Score (0-10)”
• C1: “Category”
• D1: “Total Responses”
• E1: “Promoters”
• F1: “Passives”
• G1: “Detractors”
• H1: “NPS Score”

Sample Data

Example data for rows 2-11:

• A2-A11: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10
• B2-B11: 9, 7, 10, 6, 8, 9, 5, 10, 8, 7

Formulas

• • Category Formula (Column C):

=IF(B2>=9,"Promoter",IF(B2>=7,"Passive","Detractor"))

Apply this formula to all rows in column C.

• • Total Responses (D2):

=COUNTA(B2:B11)

Adjust B11 in D2 - G2 to match the last row of your data.

• • Count Promoters (E2):

=COUNTIFS(B2:B11,">=9")

• • Count Passives (F2):

=COUNTIFS(B2:B11,">=7",B2:B11,"<=8")

• • Count Detractors (G2):

=COUNTIFS(B2:B11,"<=6")

• • Calculate NPS Score (H2):

=ROUND((E2-G2)/D2*100,0)

Optional Percentage Formulas

• Promoter % (I2): =E2/D2
• Passive % (J2): =F2/D2
• Detractor % (K2): =G2/D2

Data Validation Rule (For Score Column)

Set up data validation in column B:

• Allow: Whole Number
• Minimum: 0
• Maximum: 10
• Error Message: “Please enter a score between 0 and 10.”

Important Notes for Larger Surveys

When working with a large number of responses, adjust the cell ranges in your formulas. For example:

• Total Responses: =COUNTA(B2:B1000)
• Promoters: =COUNTIFS(B2:B1000,">=9")
• Passives: =COUNTIFS(B2:B1000,">=7",B2:B1000,"<=8")
• Detractors: =COUNTIFS(B2:B1000,"<=6")

How to Use the Template

1. Set up your spreadsheet with the suggested column headers (A1-H1).
2. Enter response IDs or customer names in column A.
3. Enter scores (0-10) in column B.
4. Use the formulas provided to calculate categories, totals, and NPS scores.

Key Formulas Explained

• Category Formula: Automatically labels each response as Promoter, Passive, or Detractor.
• COUNTIFS Formulas: Count how many responses fall into each category.
• NPS Formula: (Promoters - Detractors) ÷ Total responses × 100

Additional Tips

• Use data validation to prevent invalid scores.
• Copy the category formula down to apply it to all responses.
• The template updates automatically as you add more scores.

Is NPS Calculated Monthly or Yearly? How Often Should You Calculate NPS?

The right frequency for measuring Net Promoter Score (NPS) depends on your business type and customer interactions. Let’s explore what timing works best for different situations.

Different Measurement Approaches

• Constant Tracking: Some businesses, like e-commerce sites, track NPS constantly. Think of Amazon checking how happy you are right after each purchase – this gives them instant feedback on customer satisfaction.
• Monthly Tracking: This works well for most companies. It provides enough data to spot trends, allows time to act on feedback, and gives customers breathing room between surveys.
• Quarterly Tracking: Ideal for B2B companies or those with longer sales cycles. This schedule allows businesses to implement changes and monitor their effectiveness.
• Yearly Tracking: While yearly measurements can reveal big-picture trends, relying solely on them risks missing critical shifts in customer satisfaction over shorter periods.

Smart Implementation

Whatever frequency you choose, follow these best practices to ensure effective NPS tracking:

• Stay consistent: Stick to a regular measurement schedule to track trends accurately.
• Prevent survey fatigue: Allow at least 3 months between surveys to avoid overwhelming customers.
• Automate key surveys: Set up automatic surveys for significant customer interactions, such as purchases or support calls.
• Preserve historical data: Keep past results to track year-over-year changes and identify long-term trends.

Remember, the goal of NPS measurement is to gather meaningful insights that help improve customer satisfaction without overwhelming your audience with too many surveys.

Why is NPS Important?

Net Promoter Score (NPS) matters because it directly connects to your business success in several key ways:

Predicts Business Growth

Think of NPS as your future growth radar. When customers like your business enough to recommend it, they become your unofficial marketing team, bringing in new customers through genuine recommendations. Bain, which created the metric, reports that promoters account for more than 80% of referrals in most businesses.

Acts as an Early Warning System

NPS works like a check engine light for your business. If scores suddenly drop after a new product launch or policy change, you can spot and fix issues before they seriously impact your business.

Offers Beautiful Simplicity

With just one question, you get powerful insights. It’s easy for customers to answer and gives you a clear number to track and improve. No complex surveys or confusing metrics needed.

Boosts Your Bottom Line

Happy customers are money-savers. They stick around longer (which costs less than finding new customers) and bring in referrals (free marketing!). Even a small reduction in unhappy customers can save significant money in acquisition costs.

Guides Smart Business Moves

NPS helps you invest wisely by showing which products or services your customers value most. This insight helps prioritize improvements where they’ll have the biggest impact.

Energizes Your Team

Everyone can understand and rally behind improving an NPS score. It creates a shared mission to make customers happier and lets teams see how their work directly affects customer satisfaction.

Enables Industry Comparison

NPS lets you gauge your performance against competitors. In Qualtrics XM Institute’s 2025 study of 10,121 US consumers, the average NPS across 371 brands was 28, but industry averages ranged from 13 (utilities) to 37 (big box retailers). So compare yourself with your own industry, not with one overall number.

What’s a Good Net Promoter Score?

Rather than focusing on a single universal “good” score, it’s essential to understand NPS numbers in context. Let’s break down what NPS benchmarks mean and how they vary.

General NPS Benchmarks

There is no official scale for what counts as good. One widely used rule of thumb comes from Retently, an NPS survey vendor:

NPS range	What it means (Retently’s rule of thumb)
Above 70	Customers love you and generate a lot of word-of-mouth.
Above 30	Doing great, with far more happy customers than unhappy ones.
0 to 30	A good range to be in, with room for progress.
Below 0	More detractors than promoters, a lot of issues to address.

Factors Shaping Your Target Score

Industry Standards

Different sectors have very different norms. Average NPS by industry in Qualtrics XM Institute’s 2025 US consumer study (lowest and highest brand in brackets):

• Banks: 31 (17 to 55).
• Mobile carriers: 28 (13 to 35).
• Airlines: 26 (0 to 48).
• TV and internet providers: 16 (8 to 29).
• Utilities: 13 (-9 to 29), the lowest of the 23 industries.

Market Position

Your score also depends on who your customers are. In Retently’s 2026 benchmark, average NPS ranged from 41 to 68 across B2B industries and from 26 to 68 across B2C industries, so consumer-facing sectors vary more.

Geographic Patterns

Scoring habits also differ by region. Retently notes that:

• US: Customers give higher scores than almost anyone else.
• Europe: Customers rate companies conservatively and give fewer 9s and 10s.
• Japan: Customers tend to give lower ratings, since rating any business very high or very low is seen as poor etiquette.

If your customers are spread across regions, compare each region with its own baseline.

Typical Industry Averages

Benchmarks from different publishers are not directly comparable: B2B figures come from companies surveying their own customers, consumer figures from independent panels. Use the row closest to your business.

Industry	Average NPS	Source
B2B software and SaaS	41	Retently, 2026
Software and technology (B2B, self-reported)	51 (47 averaged over ten years of reports)	CustomerGauge, 2026
Financial services (B2B)	68	Retently, 2026
Ecommerce	61	Retently, 2026
Healthcare	37	Retently, 2026
Online retail (US consumers)	34	Qualtrics XM Institute, 2025
Banks (US consumers)	31	Qualtrics XM Institute, 2025
Mobile carriers (US consumers)	28	Qualtrics XM Institute, 2025
TV and internet providers (US consumers)	16	Qualtrics XM Institute, 2025

Focus Points

• Compare your score to direct competitors within your industry.
• Track improvements in your score over time to monitor growth.
• Watch for trends rather than fixating on a specific number.
• Consider that different customer segments may have unique benchmarks.

What is a Bad NPS Score?

Let’s cut through the confusion about what makes an NPS score concerning and what it means for your business.

When to Worry

Negative scores are an obvious red flag: they mean you have more detractors than promoters. They are also uncommon among large consumer brands. In Qualtrics XM Institute’s 2025 study of 371 US brands, the lowest score was -9, a utility.

Warning Signs

• Standing well behind your industry (for example, scoring 0 as a bank when the US bank average is 31, per XM Institute).
• Direct competitors scoring well above you.
• Being at the bottom of your market.
• Watching your score drop steadily for several months.
• Seeing sharp falls after business changes.
• Noticing seasonal dips that don’t bounce back.
• A growing share of detractors in your responses.

Real-World Picture

The weakest brands in each industry show how low scores get. Lowest brand score by industry in Qualtrics XM Institute’s 2025 US study:

• Utilities: -9.
• Hotels and room rentals: -3.
• Airlines, fast food, and social networks: 0.
• TV and internet providers: 8, in an industry that averages 16.

Age matters too: in the same study, consumers aged 18 to 24 gave brands a cross-industry average NPS of just 1.

Why These Numbers Matter

Bad NPS scores signal critical issues, such as:

• Active customer dissatisfaction.
• High risk of losing customers.
• Negative word-of-mouth spreading.
• Fundamental service or product problems.

How to Find Reliable NPS Scores Data

Here are the most trustworthy places to find company NPS scores and what to watch out for when researching them.

Best Information Sources

Industry Reports

Some of the most reliable data sources include:

• Retently’s Annual NPS Benchmarks.
• NICE Satmetrix NPS Benchmarks.
• Bain & Company’s official reports.
• Customer Guru’s NPS Tracker.

Company Reports

Many companies share their scores in:

• Annual reports (10-K).
• Quarterly earnings discussions.
• Investor materials.
• Company blog posts.

Professional Platforms

Platforms offering industry comparisons and benchmarks include:

• CustomerGauge’s industry comparisons.
• Delighted’s sector benchmarks.
• AskNicely’s industry analysis.

Major Business Publications

These outlets often cover NPS-related insights:

• Forbes.
• Harvard Business Review.
• Wall Street Journal.
• Business Insider.

Watch Out For:

• Scores can shift quickly.
• Published data might be outdated.
• Companies often broadcast only good scores.
• Different measurement methods can affect results.
• Some sources may be less reliable than others.

Smart Research Tips

• Prioritize recent data (under 1 year old).
• Cross-reference multiple sources for accuracy.
• Focus on direct competitors in your market.
• Consider company size and target market.
• Track score trends rather than fixating on single numbers.

What is the NPS of Apple, Tesla, and Amazon?

None of the three publishes an official company-wide NPS, and the figures quoted online come from third-party trackers that disagree with each other. We don’t repeat them here.

A more reliable view is the industry average from an independent panel. In Qualtrics XM Institute’s 2025 study of 10,121 US consumers, the industries these companies sit in averaged:

• Consumer electronics (brands include Apple and Amazon): 29, ranging from 8 to 47.
• Online retail (brands include Amazon.com): 34, ranging from 16 to 51.
• Automotive (brands include Tesla): 33, ranging from 11 to 52.

Context Matters

Any single company’s score can swing based on:

• Where you’re measuring: NPS differs across regions (e.g., US, Europe, or Asia).
• What you’re measuring: one product line can score differently from another.
• Who you’re asking: subscribers and occasional buyers can answer differently.
• When you’re measuring: seasonal changes or product launches can move scores.

How to Create an Effective NPS Survey

Let’s break down how to build an NPS survey that gets meaningful responses.

The Core Question

Everything starts with one key question: “How likely are you to recommend [company/product] to a friend or colleague?” Customers rate this from 0 (“Not at all likely”) to 10 (“Extremely likely”). This simplicity is what makes NPS work so well.

Getting Deeper Insights

The magic happens with the follow-up question: “Why did you give us that score?” This open-ended question turns numbers into actionable feedback. You might add 1-2 more specific questions, like:

• “What could we do better?”
• “Which features do you value most?”

But keep it brief, longer surveys get fewer responses.

Perfect Timing

Send your survey at the right moment:

• Shortly after a purchase.
• Following customer support interactions.
• A few weeks after product delivery.

Catch customers when the experience is fresh, but give them enough time to form an opinion.

Choosing Your Channel

• Email: Most common choice. Allows personalization and easy response.
• In-app/Website: Great for digital products; can trigger based on user actions.
• SMS: Works well for service businesses and gets quick responses.

Smart Design Principles

• Keep it clean and simple.
• Make it mobile-friendly.
• Use large, easy-to-tap buttons.
• Show progress indicators.
• End with a thank you.
• Stay consistent with your brand.
• Test across all devices and browsers.

Remember: A well-designed survey on your laptop might be frustrating on a phone, so always test thoroughly.

How to Run NPS Surveys on Your Website and Email

Let’s cover the two main ways to gather NPS feedback effectively.

Website Surveys

Timing and placement matter for website NPS surveys. Don’t jump on visitors right away, wait 30-60 seconds until they’ve had a chance to engage. Place surveys after key moments like:

• Completing a purchase
• Using an important feature
• Finishing a significant task

Many businesses put NPS surveys right in their customer dashboards where engaged users are more likely to respond. You don’t need complex tech, tools like Hotjar, SurveyMonkey, and Delighted make it simple to set up and analyze results.

Email Surveys. NPS Email Examples

Email remains a powerhouse for collecting NPS feedback. Keep it short and sweet with one-click scoring options.

Company-Wide NPS Email Template

Subject: Share Your Experience with [Company Name]

Dear [Customer Name],
As a valued customer of [Company Name], we’d love to hear your thoughts about your overall experience with us.

Quick Question

On a scale of 0-10, how likely are you to recommend [Company Name] to a friend or colleague?
[0] [1] [2] [3] [4] [5] [6] [7] [8] [9] [10]
Not at all likely ←–→ Extremely likely

[Click any number to continue]

Thank you for helping us serve you better.
Best regards,
[Your Name]
[Position]
[Company Name]

Product-Specific NPS Email Template

Subject: How’s your experience with [Product Name]?

Hi [Customer Name],
We noticed you’ve been using [Product Name] for [time period], and we’d love to know how it’s working for you.

Quick Question

On a scale of 0-10, how likely are you to recommend [Product Name] to someone in a similar role?
[0] [1] [2] [3] [4] [5] [6] [7] [8] [9] [10]
Not at all likely ←—-→Extremely likely

[Click any number to continue]

Your input directly influences our product development.
Thanks for using [Product Name]!
Best regards,
[Product Team Name]
[Company Name]

Making It All Work Together

Connect your survey tools with your existing systems, CRM, help desk, or customer success platforms. Many successful companies use both website and email surveys to get the full picture:

• Website surveys: Capture immediate reactions.
• Email surveys: Often reveal deeper thoughts.

Remember to integrate with your other business tools to make feedback actionable and maintain a complete view of customer relationships.

Transactional vs Relational NPS: Understanding the Key Differences

Let’s break down these two approaches to measuring customer satisfaction through NPS.

Transactional NPS: The Quick Pulse

This is your real-time feedback system, triggered by specific customer interactions. Think of it as taking snapshots of customer satisfaction right after key moments:

• Completing a purchase
• Finishing a support call
• Receiving a delivery
• Using a new feature
• Completing onboarding

For example, when you hang up from a bank’s customer service call, that immediate “How did we do?” survey is transactional NPS at work.

Relational NPS: The Big Picture

This approach looks at your overall relationship with customers. Rather than focusing on specific moments, it measures general satisfaction through periodic surveys (quarterly or twice yearly). It helps track:

• Overall brand perception
• Long-term satisfaction trends
• Customer loyalty patterns
• Market position

Think of Netflix asking how you feel about their service overall, regardless of what you watched lately.

When to Use Each Type

Transactional NPS shines when you need to:

• Fine-tune specific customer touchpoints
• Spot and fix immediate issues
• Coach specific teams
• Test new features

Relational NPS works best for:

• Strategic planning
• Tracking long-term trends
• Understanding overall loyalty
• Making company-wide decisions
• Comparing yourself to competitors

Smart Implementation

Many successful businesses use both types together. An online store might check satisfaction after each purchase (transactional) while also sending quarterly surveys about overall experience (relational).

Key Success Factors:

• Don’t overwhelm customers with too many surveys.
• Connect survey data with your customer database.
• Have clear plans for acting on feedback.
• Look for patterns across both types of responses.

Remember: You don’t have to choose just one approach. Often, combining both gives you the most complete picture of customer satisfaction.

What Can You Do With Your NPS Score? How Do You Improve Your NPS?

Let’s explore how to use your NPS data to make meaningful changes in your business.

Quick Problem Solving

NPS feedback often points to immediate issues needing attention. When you see patterns in low scores, like multiple customers mentioning slow website speeds, you’ve found a clear target for improvement. These quick fixes can boost satisfaction fast.

Guide Product Development

Your customers are telling you exactly what works and what doesn’t. When promoters rave about specific features, consider expanding them. When detractors consistently complain about something, prioritize fixing it. Think of NPS feedback as your product roadmap drawn by customers themselves.

Enhance Team Training

Share real customer feedback with your front-line staff. It helps them understand customer frustrations firsthand. If customers mention feeling rushed during support calls, you can focus training on being more patient and thorough.

Shape Business Strategy

Use NPS trends for big decisions. If scores drop after certain changes, rethink your approach. For example, a significant score drop after a price increase might signal the need to either boost value or adjust pricing.

Boost Marketing and Sales

Your happy customers are gold mines for marketing:

• Turn their experiences into case studies.
• Ask them for referrals.
• Use their success stories in marketing.
• Refine your sales pitch based on what they love.

Track Your Progress

Monitor NPS trends across:

• Different products
• Customer groups
• Regions
• Length of customer relationships

This helps spot problems and wins early.

Compare and Compete

Use industry benchmarks to understand where you stand. Being above average is a selling point; being below means there’s work to do.

Build Team Spirit

Share NPS results company-wide and celebrate improvements. Some companies even tie rewards to NPS gains, it shows customer satisfaction truly matters.

Close the Loop

Always respond to feedback:

• Thank customers who respond.
• Show them how you’re using their input.
• Personally contact unhappy customers.

Turn critics into fans by addressing their concerns.

Set Clear Goals

Instead of vague targets, make specific plans:

• Cut detractors by 15% this quarter.
• Boost promoters in key segments by 10%.
• Raise overall NPS by 5 points this year.

Remember: NPS is more than just a number, it’s your guide to building a better business.

Understanding Employee NPS (eNPS)

Think of eNPS as the internal version of your customer loyalty score. Instead of measuring if customers would recommend your product, it measures if employees would recommend your workplace.

The Core Question

Just like regular NPS, eNPS asks one key question:

“On a scale of 0-10, how likely are you to recommend [Company Name] as a place to work to a friend or colleague?”

The scoring follows the same pattern:

• 9-10: Your workplace champions.
• 7-8: Content but not excited employees.
• 0-6: Unhappy team members who might discourage others.

Why It’s Important

A strong eNPS often signals:

• People stay longer in their jobs.
• Teams get more done.
• Customers receive better service.
• Company culture thrives.
• New talent is easier to attract.

Going Deeper

After the main question, ask follow-up questions to gather actionable insights:

• “How could we make this a better workplace?”
• “What do you value most about working here?”
• “What changes would improve your day-to-day experience?”

Smart Survey Practices

• Run surveys every 3-6 months.
• Keep responses anonymous for honest feedback.
• Show employees that their input leads to real changes.
• Avoid running surveys during busy or stressful periods.

Remember: eNPS works best as part of a larger toolkit, alongside regular check-ins, company meetings, and detailed surveys.

NPS FAQ

What is the NPS scale?

NPS uses a 0–10 scale. Respondents who answer 9–10 are Promoters, 7–8 are Passives, and 0–6 are Detractors. The resulting score ranges from −100 to +100.

How do you calculate NPS?

NPS = % Promoters − % Detractors (Passives are excluded). For example, if 50% of respondents are Promoters and 20% are Detractors, your NPS is 30.

What is a good NPS score?

There is no official cutoff. Anything above 0 means more promoters than detractors. Retently’s rule of thumb treats 0 to 30 as good, above 30 as doing great, and above 70 as customers loving you. Always compare against your industry: B2B software and SaaS averaged 41 in Retently’s 2026 benchmark, while US TV and internet providers averaged 16 in XM Institute’s 2025 study.

What are promoters, passives and detractors?

Promoters (9–10) are loyal advocates, Passives (7–8) are satisfied but indifferent, and Detractors (0–6) are unhappy customers at risk of churning, model that risk with our free churn calculator.