Period calculator
Estimate your next period start date from your last period and cycle length.
Let’s run the numbers
USDTHE NUMBERS, MADE CLEARInstant calculation
＝
Your answer starts here
Check your inputs and select Calculate.
Estimates the period immediately after the entered date. Irregular cycles make predictions less reliable. Do not use this estimate for contraception or to determine pregnancy.
Common uses
Enter the first day of your last period and average cycle length to estimate your next period start date, including month, year and leap-year transitions.
BEHIND THE NUMBERSFormula & assumptions
Estimated next period start = last period start + cycle length
Estimates the period immediately after the entered date. Irregular cycles make predictions less reliable. Do not use this estimate for contraception or to determine pregnancy.