Conception Calculator
Work out the days with the highest conception probability this cycle, or reverse-engineer a likely conception window from a due date you already have.
Best days to conceive this cycle
Peak fertility days
Monday, September 7, 2026 and Tuesday, September 8, 2026
Probabilities are approximate per-cycle chances from population studies of well-timed intercourse.
How to Use the Conception Calculator
- Enter the first day of your last period and average cycle length.
- See ranked fertile days with the relative chance of conception for each.
- Optionally switch modes to estimate conception from a known due date.
Formulas Used
Highest probability: intercourse 1-2 days before ovulation (~30%+ per cycle)
Conception probability drops sharply after ovulation day (≈10%)
Estimated conception = due date − 266 days (from delivery date)
Frequently Asked Questions
Which day gives the best chance of conceiving?
Studies show the peak comes from intercourse one to two days before ovulation, giving sperm time to be waiting when the egg releases.
Can you get pregnant from sex after ovulation?
Rarely. The egg survives only 12-24 hours, so the chance falls to near zero more than a day past ovulation.
How many cycles does conception typically take?
For healthy couples under 35, about 80% conceive within six cycles and roughly 90% within a year of well-timed attempts.
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