📍 Pregnancy Due Date Calculator
Enter the first day of your last menstrual period to get your estimated due date, using the standard 40-week (280-day) dating method used by most healthcare providers.
Standard 280-day (40-week) estimate from LMP.
How the Pregnancy Due Date Calculator works
Your due date is estimated as 280 days after the first day of your last menstrual period — the same calculation (Naegele's rule) used clinically as a starting estimate.
Step-by-step calculation
- 1Enter the first day of your last period.
- 2Add 280 days (40 weeks).
Worked example
A last period starting September 1, 2026 gives a due date of June 8, 2027.
Pregnancy Due Date Calculator examples
| First day of last period | Estimated due date |
|---|---|
| Jan 1, 2026 | October 8, 2026 |
| Mar 15, 2026 | December 20, 2026 |
| Jun 1, 2026 | March 8, 2027 |
| Sep 1, 2026 | June 8, 2027 |
| Dec 1, 2026 | September 7, 2027 |
Other inputs kept at the calculator's default values. Results calculated by this calculator.
Why use a Pregnancy Due Date Calculator?
Estimate when your baby is due.
Important factors that can affect your results
- Cycle length differences.
- Ultrasound dating may change the date.
- Only about 4–5% of babies arrive on the due date.
Frequently asked questions
Is this exact?
It's a standard estimate — only about 5% of babies are born exactly on their estimated due date. An ultrasound can refine this further.
What if my cycle isn't 28 days?
This calculation assumes a standard 28-day cycle; your provider may adjust the estimate for a longer or shorter cycle.
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Last reviewed November 2026 · How we build and check our tools · Report a problem