Due Date Calculator
When is your baby due?
Enter the first day of your last menstrual period to estimate your due date, conception date, and current trimester — based on the standard 280-day rule.
Please enter the first day of your last period.
—estimated due date
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Likely conception
—
Weeks pregnant
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Trimester
How it works
- We add 280 days (40 weeks) to the first day of your last period — the standard Naegele's rule.
- Conception is estimated about 14 days after the last period, around ovulation.
- Trimesters: weeks 1–13 (first), 14–27 (second), 28 and beyond (third).
Frequently asked questions
How accurate is the due date?
It is an estimate — only about 5% of babies arrive exactly on their due date. An ultrasound may refine it.
What if my cycles are irregular?
The 280-day rule assumes a 28-day cycle, so irregular cycles make the estimate less reliable.
Is my data stored anywhere?
No — everything runs in your browser and nothing leaves your device.