How to Calculate Your Due Date

Naegele's rule estimates due date by adding 280 days (40 weeks) to the first day of your last menstrual period. It assumes a 28-day cycle with ovulation on day 14.

Step-by-step

1. Find the first day of your last menstrual period.
2. Add 7 days to the date.
3. Subtract 3 months from that date.
4. Add 1 year if needed — this is your estimated due date (EDD).
5. Alternatively: LMP + 280 days using a calendar or our Due Date Calculator.
6. Adjust for cycle length: if cycles average 32 days, add 4 days to EDD.

Tips and common mistakes

• Only 4–5% of babies arrive on the exact due date
• Term pregnancy spans 37–42 weeks
• Early ultrasound dating is most accurate before 14 weeks

Open the Due Date Calculator to apply these steps with your own numbers instantly.

Frequently asked questions