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.
Pregnancy Due Date Calculator
Verified formula Updated Jun 2026 Private — runs on your device
Verified formula
Private
Estimated due date
08 Oct 2025
- Estimated conception date
- 15 Jan 2025
- Second trimester begins
- 09 Apr 2025
- Third trimester begins
- 16 Jul 2025
For general information only — not financial, tax, legal or medical advice. Verify before you rely on it.
How to use the Pregnancy Due Date Calculator
The Pregnancy Due Date Calculator works out your estimated due date, along with 3 related figures in an instant. Enter first day of last menstrual period 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 first day of last menstrual period.
- Read off your estimated due date, together with estimated conception date, second trimester begins and third trimester begins — the calculator updates automatically, with no button to press.
Formula
The Pregnancy Due Date Calculator uses the formula:
Estimated due date = First day of last menstrual period + 280
Worked example
For example, with first day of last menstrual period of 2025-01-01, the estimated due date is 08 Oct 2025.
| First day of last menstrual period | 2025-01-01 |
|---|
| Estimated due date | 08 Oct 2025 |
|---|---|
| Estimated conception date | 15 Jan 2025 |
| Second trimester begins | 09 Apr 2025 |
| Third trimester begins | 16 Jul 2025 |
Results are estimates for educational use, not professional advice.
Frequently asked questions
This calculator uses Naegele's rule: it adds 280 days (40 weeks) to the first day of your last menstrual period (LMP) to estimate the due date.
It is an estimate. Only about 1 in 20 babies arrive on the exact due date; most are born within two weeks either side. An ultrasound dating scan can refine the estimate.
If your LMP is uncertain or your cycles are irregular, an early ultrasound is the most reliable way to date the pregnancy. Ask your doctor or midwife.
Counting from the LMP, the second trimester begins around week 14 and the third trimester around week 28. The calculator shows the approximate dates for your pregnancy.
Pick the first day of last menstrual period. Read off your estimated due date, together with estimated conception date, second trimester begins and third trimester begins — the calculator updates automatically, with no button to press.
Related guides
How to Calculate Pregnancy Due Date: Formula, Steps & Examples
Learn how to calculate Pregnancy Due Date — the formula explained step by step, with worked examples and a free calculator to check your answer.