How to use the Pregnancy Conception Calculator
This tool estimates when conception likely happened from your due date.
Open the Pregnancy Conception Calculator →
What you need to enter
- Due date
The formula
Conception ≈ due date − 266 days; the window is plus or minus 3 days.
Worked example
Using the default values in the calculator:
- Due date: 2026-10-13
| Likely conception date | Tue, 20 Jan 2026 |
| Conception window | Sat, 17 Jan 2026 – Fri, 23 Jan 2026 |
| Last period (approx.) | Tue, 06 Jan 2026 |
Tips for better results
- Treat it as an estimate.
- Sperm can survive for days.
Common mistakes to avoid
- Using it to assign paternity.
- Ignoring scan-based dating.
Please note: Health calculators and guides give general estimates, not medical advice. Talk to a doctor or other qualified professional about your own health. See our Disclaimer.