Pregnancy Due Date Calculator
Estimate the due date, how many weeks pregnant you are and the trimester dates.
Runs in your browser — your data never leaves your device.
About the Pregnancy Due Date Calculator
Doctors usually date a pregnancy from the first day of the last menstrual period (LMP), which is about two weeks before conception. A typical pregnancy lasts 40 weeks (280 days) from that date.
Enter the first day of your last period and your usual cycle length — or the conception date if you know it — to see the estimated due date, how far along you are today and the dates of each trimester. Only about 1 in 20 babies arrive exactly on the due date; most are born within two weeks either side.
How to use the Pregnancy Due Date Calculator
- Choose whether you know the first day of your last period or the conception date.
- Enter the date and, for the period method, your usual cycle length.
- Click Calculate due date.
Formula
Due date = first day of last period + 280 days (Naegele's rule), adjusted by the difference between your cycle length and 28 days.
From the conception date: due date = conception + 266 days.
Weeks pregnant are counted from the (adjusted) last period: 1st trimester to 13 weeks 6 days, 2nd trimester to 27 weeks 6 days, then the 3rd trimester.
Examples
- Last period started 1 January 2026, 28-day cycle → due date Thursday 8 October 2026.
- The same date with a 30-day cycle → 10 October 2026.
Frequently asked questions
Is this medical advice?
No. It gives a general estimate for information only. Please speak to a doctor or qualified health professional about your own situation.
Why does my scan show a different due date?
An early ultrasound measures the baby and is often more accurate than dates, especially with irregular cycles. Doctors usually go by the scan date if it differs.