Attrition Rate Calculator (period, monthly & annualized)

Understanding the attrition rate calculator — concept and principle

This calculator measures how many employees left during a period as a share of average headcount, and converts the result to a monthly and an annualized rate. It also estimates how many people were hired and the net change in headcount. HR teams use it for quarterly reports, to compare departments, and to judge whether hiring keeps pace with departures.

Leavers ÷ average headcount — with the default inputs: 29.3% a year.

How it is calculated

Average headcount = (start headcount + end headcount) ÷ 2
Attrition rate for the period (%) = leavers ÷ average headcount × 100
Annualized rate = period rate × 12 ÷ months in the period
Average monthly rate = period rate ÷ months
Hires implied = end − start + leavers; hiring rate = hires ÷ average headcount × 100
Net headcount change (%) = (end − start) ÷ start × 100

The principle

Dividing leavers by average headcount, rather than by the start figure, accounts for a workforce that grew or shrank during the period. The US Bureau of Labor Statistics expresses separations the same way: separations during the period as a percent of employment. Annualizing simply scales the period rate to twelve months, which assumes departures continue at the same pace. Hires are implied by arithmetic: to move from the start headcount to the end headcount while some people left, the gap must have been filled by new joiners.

Worked example

Defaults: 120 at the start, 126 at the end, 9 leavers, a 3-month period.

Average headcount = (120 + 126) ÷ 2 = 123.
Period attrition = 9 ÷ 123 × 100 = 7.32%, shown as 7.3%.
Annualized = 7.317 × 12 ÷ 3 = 29.3%.
Monthly = 7.317 ÷ 3 = 2.44%.
Hires implied = 126 − 120 + 9 = 15; hiring rate = 15 ÷ 123 × 100 = 12.2%.
Net change = (126 − 120) ÷ 120 × 100 = 5%.

Each point is the calculator re-run with only “Employees who left during the period” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Employees who left during the period	Attrition rate for the period
2.25	1.8%
4.5	3.7%
6.75	5.5%
9	7.3%
11.2	9.1%
13.5	11%
18	14.6%

How to read the result

Compare the annualized figure with your own history and with similar employers in your sector and country, since normal levels vary widely between industries. A rate above 100% a year means the average job was refilled more than once. Look at who is leaving as well as how many: losing new hires in their first months points to recruitment or onboarding problems, while losing experienced staff costs more knowledge.

Common mistakes

Dividing by end headcount, which understates attrition in a growing team.
Annualizing a short period with a one-off spike, such as a seasonal contract ending.
Mixing voluntary resignations with planned retirements or layoffs without saying so.

Keep in mind: Annualized figures assume the period is typical. Short periods and small teams produce volatile rates, so read them as a trend, not a verdict.

Frequently asked questions

What is the difference between attrition and turnover?

Many people use them interchangeably. Some reserve attrition for departures that are not replaced, and turnover for all departures.

How do I calculate annual attrition from monthly data?

Add the leavers for the twelve months and divide by the average headcount over the year, or multiply an average monthly rate by 12.

Should involuntary exits be included?

Include all leavers for the total rate, then report voluntary and involuntary rates separately.

Sources: U.S. Bureau of Labor Statistics, Job Openings and Labor Turnover Survey (JOLTS), definitions of the total separations rate

Checked 9 Nov 2026. Rate definition: U.S. Bureau of Labor Statistics, Job Openings and Labor Turnover Survey (JOLTS) — total separations rate = separations during the period as a percent of employment (BLS, The Economics Daily, 2024). Average headcount = mean of start and end (arithmetic).

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