Health
Estimate next period and ovulation day from cycle length and last period day
Last reviewed: How we build & verify
//
Calendar-based estimate that assumes your cycle length stays the same. Cycles commonly vary by several days, so treat the dates as approximate. Not for contraception. See a doctor if your cycles are shorter than 21 or longer than 35 days, or you miss periods.
Related Tools
Most Searched Today
Frequently Asked Questions
No. Period Calculator is free, with no signup required, and nothing you enter leaves your browser.
Period Calculator is built on published formulas and reference ranges from established health sources. We revisit it periodically as guidance evolves; the "Last reviewed" date above shows when that last happened. If something looks wrong, tell us with the feedback button in the bottom-right corner.