Estimate your most probable ovulation date and fertile window from your last period date. Not intended as a form of birth control.
Ovulation typically happens about 14 days before your next period starts, regardless of how long your overall cycle is — it's the follicular phase (before ovulation) that varies in length, not the luteal phase (after ovulation) that follows it. This calculator estimates your next period from your cycle length, then counts back 14 days to estimate ovulation.
An egg only survives 12-24 hours after release, but sperm can survive in the body for up to five days. That's why the "intercourse window for pregnancy" starts several days before the estimated ovulation date rather than on it — timing intercourse across that window, not just on the predicted day, meaningfully improves the odds of conception.
This calculator assumes a consistent cycle length, so irregular cycles will make its estimates less reliable. Tracking your actual cycle over a few months, or using basal body temperature or an ovulation kit, can help refine your personal pattern.
It's an estimate of when a home pregnancy test might reliably detect a pregnancy if this cycle resulted in conception — a few days before your next expected period, once hCG levels have had time to build up.
Pick another tool to jump straight to it.