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Due Date Calculator
Calculate your estimated due date (EDD) based on your last menstrual period.
Results
Naegele's rule: LMP + 280 days (40 weeks). EDD is an estimate — 95% of births occur between weeks 37 and 42.
📐 Due date formula
Due date = first day of last period + 280 days (40 weeks)
or: first day of last period + 1 year − 3 months + 7 days (Naegele's rule)
or: first day of last period + 1 year − 3 months + 7 days (Naegele's rule)
📊 Stages of pregnancy
| Trimester | Weeks |
|---|---|
| First | 0 — 13 weeks |
| Second | 14 — 27 weeks |
| Third | 28 — 40 weeks |
💼 Due-date scenarios
Last period on January 1
Estimated due date ≈ October 8 (approximately).
Last period on March 15
Estimated due date ≈ December 20 (approximately).
💡 Practical tips
- The date is an estimate; most births occur between weeks 38 and 42.
- An ultrasound gives a more accurate estimate.
- See your doctor or midwife for regular follow-up.
⚠️ Limits and disclaimer
- The calculation assumes a regular 28-day cycle.
- Irregular cycles make the estimate less accurate.
Official sources: Medical pregnancy-monitoring references. Consult a specialist.
Last updated: February 2026.
Last updated: February 2026.
❓ Frequently asked questions
How is the due date calculated?
By adding 280 days (40 weeks) to the first day of the last menstrual period.
What is Naegele's rule?
Add one year, subtract three months and add seven days to the date of the last period.
Is the date certain?
No, it is an estimate; most births occur between weeks 38 and 42.