Health / 03
Pregnancy Due Date Calculator
Estimate your due date from the first day of your last period, the date of conception, or an IVF embryo transfer, and see how many weeks pregnant you are, your trimester, and the key dates ahead.
Pregnancy Due Date Calculator: From the first day of your last period the page adds 280 days (Naegele's rule), moved later or earlier when your cycle is longer or shorter than 28 days. From conception it adds 266 days. After IVF it follows ACOG's guidance: 263 days after a day-3 embryo transfer and 261 after a day-5 transfer. Weeks of pregnancy are counted from the first day of the last period, as doctors and midwives count them. Runs 100% locally in your browser with zero server file uploads.
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Pick a date to see your estimated due date.
How each method counts
From the first day of the last period, the due date is 280 days, or 40 weeks, later. That assumes ovulation on day 14 of a 28-day cycle, so a longer cycle moves the date later by the difference: with a 32-day cycle it is 284 days. From a known conception date it is 266 days, and after IVF the American College of Obstetricians and Gynecologists (ACOG Committee Opinion 700, Methods for Estimating the Due Date) dates from the transfer: 263 days after a day-3 embryo transfer and 261 after a day-5 transfer. For a textbook 28-day cycle, all four methods give the same date for the same pregnancy.
The same guidance says an ultrasound in the first trimester is the most accurate way to date a pregnancy that did not come from IVF, and that the date should be changed if the scan and the period date disagree by more than a set amount. That is why the date your midwife or doctor gives you may differ from this one.
What the milestones mean
The term labels follow ACOG's definition of term pregnancy (Committee Opinion 579): early term from 37 weeks, full term from 39 weeks, late term from 41 weeks, and post-term from 42 weeks. Babies born from 39 weeks to the end of week 40 have the lowest rate of complications, which is why the weeks before 39 are no longer simply called term. To count down to the day itself, add the date to the countdown timer.
How to use it
- Choose what you know: your last period, the conception date, or an IVF transfer.
- Enter the date, and your usual cycle length if you are counting from a period.
- Read your due date, how far along you are, and the dates of each milestone.
Privacy & limitations
Everything is calculated in your browser. The dates you enter are never sent anywhere or stored.
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Frequently asked questions
How accurate is a due date?
It is an estimate. Most babies are born in the weeks around it rather than on the day. An ultrasound scan early in pregnancy dates a pregnancy more accurately than a period date, so if your midwife or doctor gives you a different date, use theirs.
Why are weeks counted from my last period, not from conception?
The first day of a period is a date most people know, while conception is usually uncertain, so pregnancy is counted from the period by convention. That is why at conception you are already about two weeks pregnant by this count.
What do early term, full term, and late term mean?
The American College of Obstetricians and Gynecologists uses early term for 37 weeks to 38 weeks 6 days, full term for 39 weeks to 40 weeks 6 days, late term for 41 weeks to 41 weeks 6 days, and post-term from 42 weeks.
When do the trimesters start?
This page follows ACOG: the second trimester starts at 14 weeks and the third at 28 weeks. Some books and apps draw the lines a week earlier or later, so you may see slightly different dates elsewhere.
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