Due Date Calculator
Estimate a due date
Enter the first day of the last menstrual period, or a known conception date, and the calculator estimates the due date using Naegele's rule (280 days from the last period, or 266 days from conception). It also shows the gestational age today, the trimester and key dates. Today is Monday, October 5, 2026.
An estimate, not advice
Only a small share of babies arrive on their due date. A healthcare provider sets the official date, often confirmed by an early ultrasound. This calculator only does date arithmetic.
How weeks are counted
Gestational age is counted from the first day of the last period, so conception happens at about two weeks.
Frequently asked questions
How is a due date calculated?
280 days after the first day of the last period.
What if I know the conception date?
Add 266 days.
Is the due date exact?
No, it is an estimate.
What if my cycle is not 28 days?
The estimate can shift; providers may adjust it.
When does the second trimester start?
At 14 weeks.
When does the third trimester start?
At 28 weeks.
When is full term?
39 weeks to 40 weeks 6 days.
Is this medical advice?
No.