Conception Date Calculator
Conception from LMP (cycle − 14) or by backing up ~266 days from a due date. Click any i for detail.
Dating
Start from
i
Mode
LMP or known due date. |
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|---|---|
First day of LMP
i
LMP
Day 1 of the period before pregnancy. |
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Typical cycle length (days)
i
Cycle
Ovulation ≈ cycle − 14; default 28. |
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Due date (EDD)
i
Due
Used when mode is due date. |
How to use this calculator
- Choose LMP or due-date mode.
- Enter the matching date (and cycle length for LMP).
- Read the conception estimate and paired due-date sketch.
- Prefer clinic/ultrasound dating when dates conflict.
Results explained
Conception is often sketched about 14 days before the next period in a typical cycle, i.e. LMP + (cycle − 14). From a due date, conception is about 266 days earlier (280 − 14). Fertilization windows span days — treat this as a calendar aid.
Quick reference: conception dating
From LMP: LMP + (cycle − 14). From due: due − 266.
| Item | Detail |
|---|---|
| 28-day cycle | Conception ~ LMP + 14 |
| Due date | LMP + 280 for classic 28-day |
| IVF | Use transfer dating from your clinic |
| Ultrasound | May adjust EDD |
Educational only — not a pregnancy test or fertility treatment plan.
How the estimate is built
conception_LMP = LMP + (cycle − 14); conception_due = due − 266; EDD ≈ LMP + 280 + (cycle − 28).
Example scenario
LMP 2026-01-01, 28-day cycle → conception ~ 2026-01-15.
FAQ
Is conception the same as intercourse day?
Sperm can live days; ovulation timing varies.
What if cycles are irregular?
Uncertainty grows — ultrasound dating helps.
Gestational vs fetal age?
Gestational age from LMP is ~2 weeks ahead of embryonic age.
See gestational age page?
Yes — for weeks-along today.