Pregnancy Calculators: Due Date, Ovulation and Milestones
From planning a pregnancy to tracking its milestones — how due dates, ovulation, conception, the trimesters and healthy weight gain are estimated, in plain language.
Conception Date Calculator
Verified formula Updated Jun 2026 Private — runs on your device
Verified formula
Private
Estimated conception date
08 Jan 2025
- Estimated last period (LMP)
- 25 Dec 2024
For general information only — not financial, tax, legal or medical advice. Verify before you rely on it.
How to use the Conception Date Calculator
The Conception Date Calculator works out your estimated conception date, along with 1 related figure in an instant. Enter estimated due date and the result updates as you type — it is free, needs no sign-up, and runs entirely in your browser so your figures stay private.
- Pick the estimated due date.
- Read off your estimated conception date, together with estimated last period (lmp) — the calculator updates automatically, with no button to press.
Formula
The Conception Date Calculator uses the formula:
Estimated conception date = Estimated due date - 266
Worked example
For example, with estimated due date of 2025-10-01, the estimated conception date is 08 Jan 2025.
| Estimated due date | 2025-10-01 |
|---|
| Estimated conception date | 08 Jan 2025 |
|---|---|
| Estimated last period (LMP) | 25 Dec 2024 |
Results are estimates for educational use, not professional advice.
Frequently asked questions
Conception is estimated about 266 days before the due date, since pregnancy is roughly 38 weeks from conception.
It is an estimate. Actual conception depends on ovulation timing, which varies, so treat the date as approximate.
The last menstrual period is estimated about 280 days (40 weeks) before the due date, the basis many due dates use.
No. Conception timing has a window of several days, so it cannot pinpoint an exact date or confirm such questions.
The Conception Date Calculator uses the formula: Estimated conception date = Estimated due date - 266. For example, with estimated due date of 2025-10-01, the estimated conception date is 08 Jan 2025.
Pick the estimated due date. Read off your estimated conception date, together with estimated last period (lmp) — the calculator updates automatically, with no button to press.
Related guides
How to Calculate Conception Date: Formula, Steps & Examples
Learn how to calculate Conception Date — the formula explained step by step, with worked examples and a free calculator to check your answer.