Churn Rate Calculator: How Many Customers You Lose

What does a churn rate of 5.00% mean?

On the defaults — 1,000 starting customers and 50 lost — the churn rate is 5.00% (ratio decimal 0.0500), which means 5 of every 100 starting customers left and 95.00% stayed. The churn rate is 50 ÷ 1,000 × 100 = 5.00%. The retention rate is 100 − 5.00 = 95.00%. A rate of 5.00% means the business keeps nineteen-twentieths of its customers in the period and must replace the twentieth it lost just to stand still — for every 100 customers at the start, 95 are still there at the end and 5 have gone. Whether that is comfortable or thin depends on how fast new customers arrive and on how steady the base is — a 5.00% rate against fast sign-ups is the usual line where a business holds its ground, and the same 5.00% against slow sign-ups still leaves the business shrinking if the loss keeps up.

Three things about the model are worth stating plainly.

First, the division is 50 ÷ 1,000 = 5.00%, and the ratio decimal is 0.0500 — the percent and the decimal are two outputs, never the same number. Second, the meaning is 5 of every 100 starting customers left — the share who went, not the share who stayed, and the retention rate is the complement. And third, the rate is displayed as a percent to two decimals, half-up, and a rate that displays as 5.01% can sit a hair above the displayed figure: 3,333 starting customers and 167 lost customers gives 5.010501%, which displays as 5.01%, and 1,234 starting customers and 57 lost customers gives 4.619125%, which displays as 4.62% — all listed in Accuracy & limitations.

The worked example, line by line

Setup: starting customers 1,000, lost customers 50.

Line 1 — the churn rate. 50 ÷ 1,000 × 100 = 5.00% (unrounded 5.000000%; ratio decimal 0.0500).

Line 2 — the retention rate. 100 − 5.00 = 95.00%.

Line 3 — the check. At 100 lost customers the rate is 10.00%; and at 99 lost it is 9.90% — below 10.00%.

Every branch, checked

Start 800: starting customers 800; lost customers 50; churn rate 6.25% (ratio decimal 0.0625); retention rate 93.75% — With 800 starting customers the rate rises to 6.25%.

Start 1,200: starting customers 1,200; lost customers 50; churn rate 4.17% (ratio decimal 0.0417); retention rate 95.83% — With 1,200 starting customers the rate falls to 4.17%.

Lost 25: starting customers 1,000; lost customers 25; churn rate 2.50% (ratio decimal 0.0250); retention rate 97.50% — With 25 lost customers the rate falls to 2.50%.

Lost 100: starting customers 1,000; lost customers 100; churn rate 10.00% (ratio decimal 0.1000); retention rate 90.00% — With 100 lost customers the rate rises to 10.00%.

Start 2,000: starting customers 2,000; lost customers 50; churn rate 2.50% (ratio decimal 0.0250); retention rate 97.50% — With 2,000 starting customers the rate falls to 2.50%.

Lost 75: starting customers 1,000; lost customers 75; churn rate 7.50% (ratio decimal 0.0750); retention rate 92.50% — With 75 lost customers the rate rises to 7.50%.

Start 500: starting customers 500; lost customers 50; churn rate 10.00% (ratio decimal 0.1000); retention rate 90.00% — With 500 starting customers the rate rises to 10.00%.

Lost 150: starting customers 1,000; lost customers 150; churn rate 15.00% (ratio decimal 0.1500); retention rate 85.00% — With 150 lost customers the rate rises to 15.00%.

The branch rates in full: 6.250000% at 800 starting customers and 4.166667% at 1,200 starting customers — both display as 6.25% and 4.17%.

The reverses, worked backwards

Smallest lost customers for the rate to REACH 10%: At the displayed 100 the figures are starting customers 1,000; lost customers 100; churn rate 10.00% (unrounded 10.000000%) (ratio decimal 0.1000); retention rate 90.00% (unrounded 90.000000%). At 99 lost customers the rate is 9.90% (unrounded 9.900000%) — below the target — so 100 is the smallest lost customers for the rate to REACH 10%.

Largest lost customers for the rate to STAY at or below 5%: At the displayed 50 the figures are starting customers 1,000; lost customers 50; churn rate 5.00% (unrounded 5.000000%) (ratio decimal 0.0500); retention rate 95.00% (unrounded 95.000000%). At 51 lost customers the rate is 5.10% (unrounded 5.100000%) — above the target — so 50 is the largest lost customers for the rate to STAY at or below 5%.

Smallest starting customers for the rate to STAY at or below 5%: At the displayed 1,000 the figures are starting customers 1,000; lost customers 50; churn rate 5.00% (unrounded 5.000000%) (ratio decimal 0.0500); retention rate 95.00% (unrounded 95.000000%). At 999 starting customers the rate is 5.005005% unrounded — above the target, though it displays as 5.01% — so 1,000 is the smallest starting customers for the rate to STAY at or below 5%.

Largest lost customers for the rate to STAY at or below 2%: At the displayed 20 the figures are starting customers 1,000; lost customers 20; churn rate 2.00% (unrounded 2.000000%) (ratio decimal 0.0200); retention rate 98.00% (unrounded 98.000000%). At 21 lost customers the rate is 2.10% (unrounded 2.100000%) — above the target — so 20 is the largest lost customers for the rate to STAY at or below 2%.

Smallest lost customers for the rate to REACH 7.5%: At the displayed 75 the figures are starting customers 1,000; lost customers 75; churn rate 7.50% (unrounded 7.500000%) (ratio decimal 0.0750); retention rate 92.50% (unrounded 92.500000%). At 74 lost customers the rate is 7.40% (unrounded 7.400000%) — below the target — so 75 is the smallest lost customers for the rate to REACH 7.5%.

Largest starting customers for the rate to STAY at or above 10%: At the displayed 500 the figures are starting customers 500; lost customers 50; churn rate 10.00% (unrounded 10.000000%) (ratio decimal 0.1000); retention rate 90.00% (unrounded 90.000000%). At 501 starting customers the rate is 9.980040% unrounded — below the target, though it displays as 9.98% — so 500 is the largest starting customers for the rate to STAY at or above 10%.

A warning about the neighbours: every neighbour above sits one customer from the star, and every neighbour rate is a hair below or above the target even though it displays as the target — a one-customer move in the starting base moves the percent by about 0.005 points, so the displayed two-decimal figure cannot tell the star from its neighbour. The page prints the unrounded six-decimal percent in full so the rounding does not mislead you: 10.000000, 9.900000, 5.000000, 5.100000, 5.005005, 2.000000, 2.100000, 7.500000, 7.400000, 9.980040.

What the defaults assume

The defaults are 1,000 starting customers and 50 lost customers — starting customers 1,000; lost customers 50; churn rate 5.00% (ratio decimal 0.0500); retention rate 95.00%. With Start 800, starting customers 800; lost customers 50; churn rate 6.25% (ratio decimal 0.0625); retention rate 93.75%. With Start 1,200, starting customers 1,200; lost customers 50; churn rate 4.17% (ratio decimal 0.0417); retention rate 95.83%. With Lost 25, starting customers 1,000; lost customers 25; churn rate 2.50% (ratio decimal 0.0250); retention rate 97.50%. With Lost 100, starting customers 1,000; lost customers 100; churn rate 10.00% (ratio decimal 0.1000); retention rate 90.00%. With Start 2,000, starting customers 2,000; lost customers 50; churn rate 2.50% (ratio decimal 0.0250); retention rate 97.50%. With Lost 75, starting customers 1,000; lost customers 75; churn rate 7.50% (ratio decimal 0.0750); retention rate 92.50%. With Start 500, starting customers 500; lost customers 50; churn rate 10.00% (ratio decimal 0.1000); retention rate 90.00%. With Lost 150, starting customers 1,000; lost customers 150; churn rate 15.00% (ratio decimal 0.1500); retention rate 85.00%. With All zero, starting customers 0; lost customers 0; churn rate undefined — no starting customers, no lost customers, and the rate is undefined. With Start 500, lost 25, starting customers 500; lost customers 25; churn rate 5.00% (ratio decimal 0.0500); retention rate 95.00% — 5 of every 100 starting customers left. With Fractional inputs (rate unrounded 5.010501%), starting customers 3,333; lost customers 167; churn rate 5.01% (unrounded 5.010501%) (ratio decimal 0.0501); retention rate 94.99% (unrounded 94.989499%) — the rate displays as 5.01%. With Start 100,000, lost 5,000, starting customers 100,000; lost customers 5,000; churn rate 5.00% (ratio decimal 0.0500); retention rate 95.00% — the same rate at one hundred times the size. With Lost 0, starting customers 1,000; lost customers 0; churn rate 0.00% (ratio decimal 0.0000); retention rate 100.00% — no customers lost at all, a real figure, not undefined. With Start 0, starting customers 0; lost customers 50; churn rate undefined — no starting customers to divide by. With Negative lost customers, starting customers 1,000; lost customers −10; churn rate −1.00% (ratio decimal −0.0100); retention rate 101.00% — the rate is below zero, a real figure. With Small numbers, starting customers 100; lost customers 5; churn rate 5.00% (ratio decimal 0.0500); retention rate 95.00% — 5 of every 100 starting customers left. With Fractional inputs (rate unrounded 4.619125%), starting customers 1,234; lost customers 57; churn rate 4.62% (unrounded 4.619125%) (ratio decimal 0.0462); retention rate 95.38% (unrounded 95.380875%) — the rate displays as 4.62%. With Over 100% (lost customers above the starting customers), starting customers 1,000; lost customers 1,200; churn rate 120.00% (ratio decimal 1.2000); retention rate −20.00% — more customers left than started, possible only if the count mixes cohorts. With Start 2,500, lost 125, starting customers 2,500; lost customers 125; churn rate 5.00% (ratio decimal 0.0500); retention rate 95.00% — 5 of every 100 starting customers left.

A note on the rounding: the rate is displayed as a percent to two decimals, half-up. With the fractional inputs the unrounded rate is 5.010501% — it displays as 5.01% — and with the other fractional inputs it is 4.619125% — it displays as 4.62%. The page prints the unrounded value so the rounding does not mislead you.

Output · formula · meaning

Who uses this

• The subscription owner counting leavers: they learn 1,000 starting customers and 50 lost is a churn rate of 5.00% — and they check the 100 reverse to see how many leavers lift the rate to 10.00%.
• The SaaS manager setting a retention target: they learn a rate of 5.00% means 95.00% stayed — and they check the 50 reverse to see how many leavers keep the rate at or below 5.00%.
• The founder reading a monthly report: they learn the rate falls when the starting base grows — and they check the 1,000 reverse to see the base that keeps the rate at or below 5.00%.
• The student learning customer metrics: they learn the churn rate is the lost customers divided by the starting customers — and they check the 75 reverse to see how many leavers lift the rate to 7.50%.

Accuracy & limitations

The math is first-principles: the churn rate is the lost customers divided by the starting customers, times 100, and the retention rate is 100 minus the churn rate — all in customers, the rate displayed as a percent to two decimals half-up, and as a ratio decimal to four decimals. There IS division in this calculator — at 0 starting customers and 0 lost customers the rate is UNDEFINED, division by zero, no starting base to divide by — the calculator shows “rate undefined” with a note, never hides it. The rate is also undefined when the starting customers are 0 for any other reason, for example 0 starting customers against 50 lost customers. At 0 lost customers the rate is 0.00% — a real figure, not undefined — and at negative lost customers the rate is below zero: −10 lost customers against 1,000 starting customers gives −1.00% (unrounded −1.000000%) — a real figure, shown with the U+2212 minus sign. Negative starting customers are NOT meaningful — a customer base is never negative — say so plainly and do not treat a negative starting figure as a real case. With the fractional inputs the unrounded rate is 5.010501% — it displays as 5.01% — and with the other fractional inputs it is 4.619125% — it displays as 4.62%. What the model cannot do is say whether 5.00% is a good churn rate: the rate says nothing about who left — losing the newest customers hurts less than losing the oldest ones — and it says nothing about when they left — the rate lumps the whole period into one number. Use it to see what share of your starting customers left — then check the customer-lifetime-value, customer-acquisition-cost and contribution-margin calculators before you decide the churn is right.

Frequently asked questions