Dates
The second date is usually today: how many weeks pregnant on that day. Due date itself is last period + 280 days. Ultrasound is often more accurate. Not a diagnosis.
Due date
How the due date is estimated
The estimated due date (EDD) is counted from the first day of the last menstrual period: add 280 days, which is 40 weeks. That is Naegele’s rule, a common obstetric estimate — not an ultrasound and not a diagnosis.
Gestational age is also counted from that period, not from conception. The conception date we show is roughly “period + 14 days”: the midpoint of a 28-day cycle, not a test result.
Trimesters: first until 13 weeks 6 days, second from week 14, third from week 28. A scan often moves the date. This page does not replace antenatal care.
Naegele’s rule
Due date = first day of last period + 280 days. Example: period on 1 January 2026 → due 8 October 2026. On 1 April 2026 that pregnancy is 12 weeks 6 days (90 days), still the first trimester.
Cycles longer or shorter than 28 days shift ovulation; this tool does not adjust for cycle length.
Gestational age = days since the last period. Conception ≈ period + 14 days.
How to estimate a due date
- Enter the first day of the last period: The first day of bleeding, not the last day and not the day of a pregnancy test.
- Choose the day to measure from: Defaults to today. Change it only if you want the week on another day. The due date does not change.
- Read due date, week and trimester: You also get a conception midpoint. Treat it as an estimate.
Frequently asked questions
Why 280 days, not nine months?
Forty weeks from the last period is the obstetric convention. Calendar “nine months” is fuzzier because months are different lengths.
Is the conception date exact?
No. Period + 14 days assumes a 28-day cycle. Ovulation varies. Treat it as a midpoint.
My ultrasound disagrees.
An early scan often dates better than the last period. Follow the clinician, not this page.
IVF or an irregular cycle?
Naegele from the last period is a poor fit. Use the transfer or ovulation date your clinic gave. This tool does not model IVF.