Period Calculator
Estimate the next period start from the last start date and your usual cycle length.
Formula
Next start = last start date + cycle length in calendar days.
First day of last period = 2026-10-01 · Usual cycle length (days) = 28
How to use
- Enter the first day bleeding began.
- Enter the usual start-to-start interval.
- Read the estimated next start.
Examples
- January 1 with a 28-day cycle: January 29.
Frequently asked questions
Do I count from the end of bleeding?
No. Cycle length runs from the first day of one period to the first day of the next.
Is this reliable contraception?
No. Cycles can vary; the date does not establish ovulation, pregnancy or safe days.
Does this replace medical advice?
For information only; it does not replace a doctor or individual assessment.
Sources
Updated: