Pregnancy Calculator
Calculate the estimated due date and gestational age from the first day of your last menstrual period.
- Estimated conception date
- October 04, 2026
- Total days pregnant
- 0
- Current trimester
- 1st trimester
- Days until due date
- 279
How the due date is calculated
The calculator uses Naegele's rule: it adds 280 days (40 weeks) to the first day of your last menstrual period, adjusting the result based on the average cycle length you enter.
The estimated conception date is calculated by adding 14 days to the adjusted last menstrual period date, and the gestational age is the difference between today and that date, expressed in complete weeks and days.
Frequently asked questions
How is the estimated due date calculated?
We add 280 days (40 weeks) to the last menstrual period date, adjusted by cycle length, following Naegele's rule used by obstetricians.
Why does cycle length affect the result?
Cycles longer or shorter than 28 days shift the actual ovulation date, so we adjust the last menstrual period date proportionally to better estimate conception and delivery.
Is the due date exact?
No. It's an estimate based on statistical averages; only about 5% of births happen exactly on the calculated date. First-trimester ultrasounds usually refine this estimate.
How are trimesters defined?
The 1st trimester runs through week 13, the 2nd from week 14 to 27, and the 3rd trimester starts at week 28 until delivery.
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