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Due Date Calculator

Estimate your pregnancy due date from your last period, conception date, ultrasound, or IVF transfer — with the estimated conception date and early, full, and late-term windows.

days

Days from the start of one period to the next (default 28).

Estimated due date

October 8, 2026

Estimated conception date
January 15, 2026

Term windows

TermBegins
Early term (week 37)September 17, 2026
Full term (week 39)October 1, 2026
Late term (week 41)October 15, 2026
Post-term (week 42)October 22, 2026
Estimated due dateOctober 8, 2026View results

Estimate your pregnancy due date from whatever information you have — the first day of your last period, a known conception date, an ultrasound measurement, or an IVF transfer date. The calculator also shows your estimated conception date and the dates each term window begins.

Formula

Every method resolves to a single estimated due date (EDD):

Last period:  EDD = last period + 280 days + (cycle length - 28)
Conception:   EDD = conception date + 266 days
Ultrasound:   EDD = scan date + (280 - gestational age at scan)
IVF transfer: EDD = transfer date + 266 - embryo age (e.g. 261 for day 5)
A pregnancy is dated from the last menstrual period, which is about two weeks before conception — so it lasts 40 weeks from your period but 38 weeks from conception.

Term classifications

TermGestational age
Early term37–38 weeks
Full term39–40 weeks
Late term41 weeks
Post-term42 weeks and beyond

Examples

Last period on January 1, 2026 (28-day cycle)

EDD = January 1 + 280 days = October 8, 2026, with an estimated conception date of January 15, 2026. Full term begins October 1, 2026.

Day-5 IVF transfer on January 15, 2026

EDD = transfer + 261 days = October 3, 2026.

Frequently asked questions

How is a due date calculated?
The standard method (Naegele's rule) adds 280 days — 40 weeks — to the first day of your last menstrual period. From a known conception date it's 266 days (38 weeks), since conception happens about two weeks after the last period began.
How accurate is a due date?
It's an estimate. Only about 4% of babies are born on their exact due date, roughly 60% arrive within a week of it, and almost 90% within two weeks. An early ultrasound is generally the most accurate way to date a pregnancy.
What do early, full, and late term mean?
Babies born at 37–38 weeks are early term, 39–40 weeks are full term, 41 weeks are late term, and 42 weeks or more are post-term. The term window table shows the date each of these stages begins for your pregnancy.
How does cycle length change the due date?
The last-period method assumes ovulation around day 14. If your cycle is longer or shorter than 28 days, ovulation shifts, so the calculator moves the due date by the difference between your cycle length and 28 days.
How is an IVF due date different?
With IVF the conception timing is known exactly, so the due date is the transfer date plus 266 days minus the embryo's age. A day-5 (blastocyst) transfer adds 261 days, a day-3 transfer adds 263 days, and a day-6 adds 260.

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