# What Is Customer Churn? How to Measure Retention

- URL: https://girisimcikafasi.com/en/blog/what-is-customer-churn/
- Published: 2026-10-24
- Updated: 2026-10-24
- Category: Starting and growing a business
- Publisher: Girişimci Kafası

On 10 February 1806 a ship left Boston harbour for Martinique with a hold full of pond ice. The Boston Gazette noted: "No joke. A vessel has cleared at the Custom House for Martinique with a cargo of ice. We hope this will not prove a slippery speculation." Her owner was 23-year-old Frederic Tudor. Much of the ice melted on the three-week voyage, and with no storage on the island the rest soon melted too. Tudor came home from that first venture about $4,500 down.

The real lesson came fifteen years later. By then Tudor had built a double-walled ice house in Havana and was selling in Charleston and Savannah. In a letter to Stephen Cabot dated 5 February 1821, the picture was grim: he had thought himself a rich man and was now almost bankrupt. In Havana, his best market, sales had fallen by half; in Charleston and Savannah by a third. In Martinique they had lost $25,000 in three years, and he wrote of giving the business up.

He did not. According to a bulletin published by Baker Library in 1932, Tudor taught people how much more refreshing cold drinks were than warm ones by selling both at the same price. On 4 August 1852, just short of his 69th birthday, he summed up half a century of trading in three points: wherever ice had been introduced it had failed at first; then, everywhere, profit had come and demand had grown "with time & habit".

Tudor's problem was never the first sale. It was whether the same customer would want ice again next summer.

## What is customer churn?

Customer churn is the share of customers who stop using or paying for your product in a given period. The sum is simple: divide the number of customers who left during the period by the number you had at the start. If you began the month with 200 customers and 10 left, your monthly churn is 5%. Retention is the other side of the same coin.

Five per cent sounds small, but it repeats every month. A company losing 5% a month keeps only 54% of its starting customers by the end of the year. Almost half of every effort you spend winning customers melts away within a year, like the ice in Tudor's hold.

## Measuring retention properly

Writing for Failory, Enzo Avigo calls retention rate the best indicator of product-market fit. Sign-ups and sales can be inflated by a good marketing push; retention shows whether people stay, keep using the product and keep paying. Measured badly, though, it lies too.

### Choose a time window that fits your business

Avigo's example is Zapier. The product is built to be set up and then left to run; nobody needs to open it every day. If Zapier tracked daily active users, it would look far less successful than it is. Measuring a weekly product daily shows you churn that isn't there. Avigo also refuses to count two weeks of activity as retention; he prefers to look at the three-month mark.

### Measure from sign-up

The most common mistake, in Avigo's view, is measuring retention from the moment someone starts properly using the product. The chart looks better that way, because those who leave straight after signing up drop out of the sums. Yet those early exits tell you where your positioning or first experience is breaking.

### Split customers into cohorts

Track the customers who arrived in the same month as one group, a cohort, and you can see the effect of each change you make. Avigo does not expect statistical certainty from small startups, but suggests around 50 people in a cohort as a rough floor, so you are not reshaping the product on the evidence of three users.

### Compare yourself against the right benchmark

According to a benchmark Avigo cites from Lenny's Newsletter, three-month retention above 30-40% is a good sign for consumer software, and closer to 50% for software sold to businesses.

## To reduce churn, understand who stays

Tudor's same-price trick was an early version of what is now called the "aha moment". Avigo describes it as the moment a user first grasps the value of a product. His guess for Zapier is creating the first automation, not opening the builder; for Loom, recording the first video, not installing the extension. If users leave before reaching that moment, the leak is not in the product itself but in the path to it.

The second step is to look past the depressing part of the chart to the hopeful one. Avigo notes that early companies panic when they see 96% of users gone. Yet the remaining 4% often hide a small group that is remarkably loyal. Look at who they are, what they do for a living and which part of the product they use. Then build for them.

As Avigo tells it, the positioning expert April Dunford started her career this way. Before shutting down a product that wasn't taking off at the startup where she worked, she talked to customers and found that a small group was using it in a way nobody had expected. The company repositioned the product for that market and sales took off.

Finally, talk to those who leave. As Dunford warns, when positioning is unclear people arrive thinking the product is something else, and they leave at the first contact. In that case the problem lies not in the product but in how you describe it.

## Holding, having, churning

Retention comes from the Latin retinere: re-, "back", and tenere, "to hold". Habit comes from the Latin habitus, which in turn derives from habere, "to have, to hold". The two words say the same thing: what you hold on to is what you have grown used to.

Churn comes from humbler origins. In Old English, cyrin was the vessel in which milk was agitated to make butter. Today the word describes customer attrition in business, and in telecoms the crowd ready to switch provider. With every turn a churn separates two things: one stays, the other drains away. Your job is to know why the part that stays, stays.

## Final word

In the second book of The Art of Love, the Roman poet Ovid, explaining how a new bond becomes a lasting one, left two lines that could sit in any founder's notebook:

> "Fac tibi consuescat: nil adsuetudine maius: / Quam tu dum capias, taedia nulla fuge."

Let them grow used to you; nothing is stronger than habit. Until you have won it, shrink from no effort.

Tudor was selling habit, not ice. Three months from now, how many of today's customers will still be with you, and do you know why the ones who stay, stay?

*To understand what your loyal customers are telling you, [What Is Product-Market Fit?](https://girisimcikafasi.com/en/blog/what-is-product-market-fit/) is worth a read.*