Pregnancy Due Date Calculator
Calculate your estimated due date, see how many weeks pregnant you are, and follow your pregnancy week by week.
How is a due date calculated?
The calculator uses Naegele's Rule, the standard method in obstetrics. It counts 280 days (40 weeks) from the first day of your last menstrual period.
Think of it as a due month
Babies don't keep to a calendar. A full-term birth can happen anywhere from 37 weeks, 0 days to 41 weeks, 6 days, so it helps to treat your due date as a rough marker rather than a deadline.
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Due date calculator FAQ
How is my due date calculated?
Using Naegele's Rule: 280 days (40 weeks) from the first day of your last menstrual period. From a known conception date we add 266 days; from an IVF transfer we add 263 days for a day-3 embryo or 261 days for a day-5 blastocyst.
How accurate is a pregnancy due date?
It's an estimate. Only around 1 in 20 babies arrive on their exact due date. Most are born within two weeks either side, and anywhere from 37 to 42 weeks counts as term.
How many weeks pregnant am I?
Pregnancy is counted from the first day of your last period, not from conception. That means you're already considered about two weeks pregnant on the day you conceive, and around four weeks pregnant when your period is missed.
Can my due date change after an ultrasound?
Yes. A first-trimester dating ultrasound is the most accurate way to date a pregnancy. If its measurements differ noticeably from your period-based date, your provider may update your due date.
What if my cycles are irregular or longer than 28 days?
The LMP method assumes a 28-day cycle with ovulation around day 14. If your cycles are longer, shorter, or irregular, a conception date or an early ultrasound will usually give a more reliable estimate.
Not sure yet? Try our pregnancy test quiz or read about early pregnancy symptoms.