Due date from your last period, conception or IVF transfer, with weeks pregnant today
Runs in your browser. Nothing you type is sent anywhere. Checked against sources on 29 Sept 2026.Pregnancy Due Date Calculator adds 280 days to the first day of your last period, adjusted by the difference between your cycle and 28 days. From a conception date it adds 266 days, and from an IVF transfer 263 days for a day-3 embryo or 261 for a day-5 embryo, following ACOG guidance.
Under "Method", pick Last period, Conception or IVF transfer, whichever date you know.
Enter that date in the box below it, such as "First day of your last period".
For Last period set "Usual cycle length"; for IVF transfer pick Day 3 or Day 5 (blastocyst).
Read the Estimated due date, the weeks pregnant today and the Trimester, and open Key dates for each milestone.
Press Share result to copy a link with these dates.
A due date is a dating convention, not a forecast. The one most people are given comes from Naegele's rule: 280 days, or 40 weeks, from the first day of the last menstrual period. That rule assumes a 28-day cycle with ovulation around day 14, so this page moves the date by one day for every day your regular cycle runs longer or shorter than 28. A 32-day cycle gives a due date four days later.
Two other starting points are offered. From a known conception date the due date is 266 days on, the same 38 weeks with the two pre-ovulation weeks removed. After IVF, the American College of Obstetricians and Gynecologists (Committee Opinion No. 700) dates the pregnancy from the embryo's age at transfer: 263 days after a day-3 transfer and 261 days after a day-5 transfer.
Whichever you use, the page shows today's count in weeks and days, the trimester, the days left, and a table of milestones with their calendar dates. The trimester lines follow ACOG: the second begins at 14 weeks 0 days and the third at 28 weeks 0 days. Some bodies, including the NHS, draw them a week earlier, so a leaflet may disagree with this page by a week without either being wrong. The term labels come from ACOG Committee Opinion No. 579: early term from 37 weeks, full term from 39, late term from 41 and postterm from 42.
What this tool does not do matters more than what it does. It cannot see the pregnancy. A first-trimester ultrasound is the most accurate way to date one, and once a clinician has set a date from a scan, that date replaces anything worked out here. The period method is unreliable for irregular cycles, after recent hormonal contraception, or when the date of the last period is uncertain. Most babies are not born on their due date; a normal pregnancy runs anywhere from 37 to 42 weeks.
This page gives general information and is not medical advice. Questions about your pregnancy belong with your midwife, doctor or fertility clinic. The dates you enter stay in your browser.
Naegele's rule adds 280 days, or 40 weeks, to the first day of the last period. A last period starting on 1 January 2026 gives a due date of 8 October 2026. For a regular cycle longer or shorter than 28 days, the date moves by the difference, so a 32-day cycle adds four days.
The first day of a period is a date most people know, while the day of conception usually is not. Counting from the period adds about two weeks before conception, so at 8 weeks pregnant the embryo is roughly 6 weeks old. Scans and antenatal notes use the same period-based count.
ACOG Committee Opinion No. 700 dates an IVF pregnancy from the embryo transfer. The due date is 263 days after transferring a day-3 embryo and 261 days after a day-5 blastocyst. A frozen transfer uses the same offsets, counted from the transfer date rather than from any period.
On the ACOG lines used here, the first trimester runs to 13 weeks 6 days, the second from 14 weeks 0 days to 27 weeks 6 days, and the third from 28 weeks 0 days. The NHS and some other sources start each trimester about a week earlier, so leaflets can differ.
Use the scan date. ACOG describes a first-trimester ultrasound as the most accurate way to date a pregnancy, and a clinician who has redated a pregnancy from a scan has already replaced the period-based estimate. This page is a starting estimate for before that appointment, not a substitute for it.
ACOG Committee Opinion No. 579 labels a pregnancy early term from 37 weeks 0 days, full term from 39 weeks 0 days, late term from 41 weeks 0 days and postterm from 42 weeks 0 days. The milestone table on this page gives the calendar date on which each label begins.
Rates and rules change; check the source before you rely on a figure.
Still stuck? Ask about Pregnancy Due Date Calculator and anybody who knows can answer. No account needed.
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