Customer retention rate formula with a simple example

The customer retention rate formula is `((End customers − New customers acquired during the period) ÷ Start customers) × 100`. It shows what share of the customers you started with were still customers at the end, after you remove customers who were newly acquired during that same period. This formula works for a defined reporting window, like a month or quarter, but it stops being useful if your system counts customers differently at the start and end, or if your CRM treats reactivated, paused, merged, or duplicate accounts in a way that changes the meaning of the numbers.

The formula you can use right away

Use this version of the customer retention rate formula:

((End customers − New customers acquired during the period) ÷ Start customers) × 100

Where:

• Start customers = the number of customers you had at the beginning of the period
• End customers = the number of customers you had at the end of the period
• New customers acquired during the period = customers who first joined during that period

The subtraction matters because you want to measure how many of the original customers stayed, not how many total customers you had at the end.

For example, if you started with 200 customers, ended with 210 customers, and 50 of those were new during the month, the formula uses 210 − 50 = 160 as the retained customer count before dividing by the 200 you started with.

A simple example with numbers

Say you started the month with 200 customers.

During the month, you acquired 50 new customers. At the end of the month, you had 210 customers total.

Plug the numbers into the formula:

((210 − 50) ÷ 200) × 100 = (160 ÷ 200) × 100 = 80%

So your customer retention rate for that month is 80%.

That means 160 of the 200 customers you started with were still customers at the end of the month.

What counts as a retained customer

The most common mistake is counting new customers as retained customers. You should not do that. Retention measures how many starting customers stayed, so new customers are removed from the ending count before you divide.

A few practical rules help keep the math clean:

• Count a customer as retained only if they were active at the start and still active at the end.
• Do not count customers who joined during the period as retained for that same period.
• If a customer churned and later returned during the same period, your CRM may treat them as retained, reactivated, or new, depending on its rules. Use the definition in your reporting source, not a guess.
• If your CRM defines accounts differently from customers, use the same unit in both the start and end counts.

The key boundary is this: the formula only answers retention for the customer set you define. It does not tell you whether an account was profitable, active in a product, or retained in a different system unless your reporting source uses that exact definition.

When the formula needs a second look

The formula itself stays simple, but the inputs can get messy.

Check the current reporting rules in your CRM or billing system if any of these apply:

• Subscription pauses or freezes
• Account merges or duplicate records
• Customers who downgrade but do not fully cancel
• A changed measurement window, such as moving from monthly to quarterly reporting

If the reporting period changes, use the same logic across both ends of the period. A longer window will often change the retention result because more customers have time to leave, pause, or return. If your system defines the period differently from your dashboard, match the source definition before you compare numbers.

When the period changes, recheck three things before you trust the result: the start count, the end count, and which customers are labeled new inside that window. A month-to-month retention rate is not directly comparable to a quarterly rate unless the underlying method is the same.

Quick way to verify your result

A fast sanity check is to see whether the answer is plausible before you publish it in a dashboard.

If the end customer count is lower than the start count, retention should usually be below 100% once new customers are removed. If the result is above 100%, that usually means one of two things: either you gained more returning or counted customers than you lost, or the CRM definition is not the one you think it is.

Before using the number, confirm that the customer definition matches the reporting source. If your dashboard counts active subscriptions, but your spreadsheet counts paying accounts, the retention rate can look right mathematically and still be wrong for the business question you meant to answer.