Conception Calculator
Calculate best times for conception and fertility tracking. Free, fast, accurate — no signup, mobile-friendly, works in
Calculation Method
Date Information
Expected delivery date provided by your healthcare provider
Important Notes
- • Conception typically occurs during ovulation (14 days after LMP)
- • Sperm can survive 5 days, egg survives 24 hours
- • Due dates are estimates - only 5% of babies are born on their exact due date
- • These calculations are for educational purposes only
- • Consult your healthcare provider for medical advice
Calculate conception date from due date
Conception Date
Most likely conception date
Conception Window
Due Date
Estimated delivery date (40 weeks)
Current Week
Gestational age
Trimester
Current trimester
Fertility Window
The 6-day window when conception is most likely to occur
Fun Facts
How it works
A conception calculator estimates when conception likely occurred and the fertile window, working back from your last period and cycle length. Ovulation typically happens about 14 days before the next period, and conception occurs around then.
Conception timing
Ovulation ≈ LMP + (cycle length − 14 days) Conception ≈ due date − 266 days
- LMP
- first day of last menstrual period
- cycle length
- days between periods (often ~28)
Worked example
- LMP = March 1
- 28-day cycle
- Ovulation ≈ March 1 + (28 − 14) = March 15
Likely conception around March 15, give or take a few days.
Good to know
- Sperm can survive ~5 days, so the fertile window spans several days before ovulation.
- Cycle length varies, so this is an estimate — ovulation tests pinpoint it better.
- Conception date differs from gestational age, which is measured from the LMP.
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Frequently Asked Questions
When during the cycle is conception most likely?
During the fertile window: the five days before ovulation plus ovulation day itself. Sperm can survive up to about five days in the reproductive tract, while the egg is viable for roughly 12–24 hours after ovulation.
How does the calculator estimate a conception date?
Working back from a due date, conception is estimated at about 266 days (38 weeks) before it — pregnancy is dated 40 weeks from the last menstrual period, but fertilization typically occurs about two weeks after that period starts.
How accurate are conception date estimates?
They are approximations: cycle lengths vary, ovulation does not always occur on day 14, and sperm survival means intercourse up to five days before ovulation can lead to conception. An early ultrasound gives the most reliable dating of a pregnancy.
How can I track ovulation more precisely?
Ovulation predictor kits detect the LH surge about 24–36 hours before ovulation, basal body temperature rises slightly after ovulation, and cervical mucus becomes clear and stretchy near it. Combining methods over a few cycles gives the clearest picture.
When should I talk to a doctor about conceiving?
General guidance is to see a provider after 12 months of trying without success if under 35, or after 6 months if 35 or older — and earlier if you have irregular cycles or known reproductive conditions. Preconception checkups are worthwhile for everyone planning a pregnancy.