Conception · Ovulation

When are you most likely to conceive?

Based on your cycle, here's the six-day fertile window — the only days in any cycle when conception is possible.

First day of last period
Average cycle length · days
28
21–35 days is typical · 28 is the average
Most likely ovulation day
June 2in 9 days
Fertile window: May 28 – Jun 3
Your cycle, visualized
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PeriodFertile windowOvulation
If you conceive this cycle

Estimated due date:

February 23, 2027

That's roughly 9 months from today.

How accurate is this, honestly?
Accuracy±2 days

Ovulation prediction from cycle math alone is right within ±2 days about 60% of the time. Real bodies don't run on calendars — Wilcox et al. (1995, NEJM) showed that the fertile window can span days 6–21 of a cycle even among women with regular periods.

The window we show is the canonical 6-day fertile window (5 days before ovulation through ovulation day), with peak per-cycle conception probability ~24–48 hours before ovulation. After ovulation, an egg survives only ~12–24 hours; sperm can live up to 5 days in fertile cervical mucus — that asymmetry is why "the day before" matters more than "the day of."

For higher accuracy, pair this with basal body temperature tracking, LH ovulation test strips, or cervical mucus monitoring — or all three. If you've been trying for 12+ months without success (or 6+ if you're over 35), that's the signal to talk to a doctor.

Sources: Wilcox AJ, Weinberg CR, Baird DD. N Engl J Med 333:1517–21 (1995), "Timing of sexual intercourse in relation to ovulation"; Stanford JB & Mikolajczyk RT. Am J Obstet Gynecol 187:1340–4 (2002); ASRM Practice Committee, "Optimizing natural fertility" (2017).

Read the full methodology →
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