Conception Date from Due Date
Estimated conception window = due date − 266 days, ± a few days for fertile window. Not medical advice.
Result
Estimated conception
2026-01-22
Window: 2026-01-17 → 2026-01-23.
- Due date2026-10-15
- Estimated conception2026-01-22
- Conception window2026-01-17 → 2026-01-23
- Implied LMP (-280d)2026-01-08
Step-by-step
- Conception ≈ due − 266 days = 2026-01-22.
- Window allows for fertile window: 5 days before to 1 day after.
How to use this calculator
- Enter due date.
- Read estimated conception date and window.
About this calculator
Working backwards from a due date: subtract 266 days for estimated conception. The window extends 5 days earlier (sperm survival) through 1 day later (egg survival). Useful when paternity questions arise — but this is a formula tool only, not clinical or legal evidence.
Frequently asked
Usually 6 days: 5 days before through ~1 day after ovulation. Conception is most likely on the ovulation day or 1-2 days before.
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