Calculator Pregnancy
Due date calculator
Your estimated due date is a target, not a deadline — only about 1 in 20 babies arrive on it. Enter one date below for your due date and exactly how far along you are today.
Estimated due date
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By the numbers Context
How your due date is calculated
The standard estimate counts 280 days — 40 weeks — from the first day of your last menstrual period. This is Naegele’s rule, and it assumes a regular 28-day cycle with ovulation around day 14, which is why the calculator lets you adjust for your own cycle length. Counting from your last period, rather than from conception, is simply the convention clinicians use because the period is a date most people can pin down.
A due date is an estimate, not a deadline. Only around 5% of babies are born on the exact date, and a full-term birth is anything from 37 to 42 weeks. The most accurate dating comes from an ultrasound in the first trimester, which measures the baby directly — so if your clinician gives you a date based on a scan, that is the one to trust.
40 weeks
a full-term pregnancy, counted from your last period
ACOG
~5%
of babies actually born on their exact due date
Research
280 days
the standard estimate from the last menstrual period
Naegele’s rule
Sources: American College of Obstetricians and Gynecologists (ACOG); standard obstetric dating (Naegele’s rule).
Frequently asked questions
How is my due date calculated?
It is estimated as 280 days (40 weeks) from the first day of your last menstrual period, adjusted for your cycle length. You can also calculate it from a conception date (add 266 days) or an IVF transfer date, which this calculator supports.
How many weeks pregnant am I?
Your weeks of pregnancy (gestational age) are counted from the first day of your last period, not from conception. This calculator shows how far along you are today alongside your estimated due date.
Is a due date based on 39 or 40 weeks?
The due date itself is set at 40 weeks from your last period. “Full term” is now defined as 39–40 weeks, with 37–42 weeks all considered a normal time to give birth.
How accurate is a due date?
It is an estimate — only about 5% of babies arrive on it. A first-trimester ultrasound is the most accurate way to date a pregnancy and may adjust the date from the last-period calculation.
Can I calculate my due date from conception?
Yes. If you know your conception date, your due date is roughly 266 days later. This calculator includes a conception-date option, as well as IVF day-3 and day-5 transfer dating.