Due Date Calculator
Quick answer
Enter the first day of your last menstrual period to estimate your due date, how many weeks along you are today and your current trimester — using Naegele’s rule, the standard method used by midwives and doctors.
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Naegele’s rule
Due date = first day of last period + 280 days (40 weeks)
Conception ≈ last period + (cycle length − 14) days
Longer or shorter cycles shift the due date by the difference from 28 days
Trimesters: 1st weeks 1–13 · 2nd 14–27 · 3rd 28–40
Only about 4–5% of babies arrive exactly on their due date — most arrive within two weeks either side.
Worked example
- 1
Last period started March 1.
- 2
Due date = March 1 + 280 days ≈ December 6.
- 3
Estimated conception ≈ March 15.
- 4
Eight weeks after March 1, you are 8 weeks pregnant — first trimester.
Interpreting your due date
| Your result | Category | What it means |
|---|---|---|
| 40 weeks (280 days) from your last period | Estimated due date | Only about 1 in 20 babies arrives on the exact date — most come within two weeks either side. |
| Weeks 1–13 | First trimester | Counted from your last period, so conception happens around “week 2”. Morning sickness is common early on. |
| Weeks 14–27 | Second trimester | Many women feel their best here. A dating ultrasound at 8–13 weeks gives the most reliable estimate. |
| Weeks 28–40 | Third trimester | The baby gains weight quickly — growth checks and your provider’s delivery plan matter most now. |
Frequently asked questions
Sources & further reading
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Open calculatorThis calculator provides general estimates for informational purposes only and is not medical advice. For personal guidance, consult a qualified healthcare provider.