How accurate is the due date?

Only about 4% of babies arrive exactly on the estimated date — most are born within two weeks of it. It is a midpoint, not a deadline.

What if my cycle is irregular?

Longer or shorter cycles shift ovulation, so enter your average cycle length for a better estimate, or rely on first-trimester ultrasound dating.

Which weeks are which trimester?

Weeks 1–13 are the first trimester, 14–27 the second, and 28 to birth the third.

All calculators

Pregnancy Due Date Calculator

Estimate your baby's due date based on your last period or conception date (Naegele's rule).

Calculation methodFirst day of last period

Select a date to estimate your due date and pregnancy timeline.

Formula

Due date = first day of last period (LMP) + 280 days (Naegele's rule)

How to calculate

1Note the first day of your last menstrual period.
2Add 280 days (40 weeks) for the estimated due date.
3Count back 3 months and add 1 year for a quick mental check.
4Ultrasound dating in the first trimester refines this estimate further.

How to use this calculator

1Choose your calculation method — last period, conception date or ultrasound date.
2Enter the relevant date and your average cycle length if known.
3See your estimated due date and current week instantly.
4The timeline updates trimester milestones as you go.

Examples

LMP example

Last period starting March 10 → estimated due date around December 15 (280 days later).

Conception example

Conception on April 1 → due date around December 26 (266 days later).

Common questions

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