Free Tools
Due Date Calculator
Estimate your delivery date from your last period, conception date, or IVF transfer.
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How this works
Pick the date you know best — most people start with the first day of their last menstrual period (LMP), which is also how clinicians date pregnancies. If you tracked ovulation or know your conception date, that's even more precise. For IVF pregnancies, use the embryo transfer date and tell us whether the embryo was transferred on day 3 or day 5.
The calculator runs the standard formula on whichever date you picked. Your estimated due date (EDD), current gestational age in weeks and days, current trimester, and days remaining all update instantly — no submit button, no page reload.
Most full-term pregnancies last between 37 and 42 weeks. Only about 5% of babies arrive exactly on their estimated due date; healthy births happen anywhere in that window. Your provider may adjust your due date after a first-trimester ultrasound if measurements differ by more than seven days.
The math behind it
LMP mode uses Naegele's rule: add 280 days (40 weeks) to the first day of your last menstrual period. This assumes a regular 28-day cycle with ovulation on day 14. If your cycle is consistently longer or shorter, the actual due date may shift by a few days.
Conception mode adds 266 days (38 weeks) to your stated conception date. Pregnancy duration is more accurately measured from conception than from LMP — clinicians use LMP as a proxy because it's easier to remember.
IVF mode subtracts the embryo's age at transfer from 266 days, then adds the remainder to your transfer date. For a day-3 transfer that's transfer + 263 days; for a day-5 (blastocyst) transfer it's transfer + 261 days. This is the ASRM-recommended method.
All three methods give an estimate — your healthcare provider's first-trimester ultrasound is the most accurate dating method available and may revise your EDD.
Frequently asked questions
Due date calculators are estimates. About 5% of babies arrive on the exact estimated date; most arrive within two weeks before or after. A first-trimester ultrasound (typically 8-13 weeks) is the most accurate method to date a pregnancy and may revise the due date provided here.
Naegele's rule assumes a 28-day cycle. If your cycles are consistently longer than 28 days, your true due date is likely a few days later than this calculator estimates; if shorter, a few days earlier. For more accuracy, use the conception-date mode or wait for your first-trimester ultrasound.
Use whichever you know better. LMP is more commonly remembered and is the dating standard for obstetric care. Conception date is more precise when you've been tracking ovulation, used at-home ovulation tests, or had a planned conception cycle.
For IVF pregnancies, the embryo's age at transfer matters because the developmental clock starts at fertilization, not at the transfer date. A day-3 embryo at transfer is already 3 days old, so EDD = transfer + 263 days. A day-5 blastocyst is 5 days old, so EDD = transfer + 261 days.
Yes. Your healthcare provider may revise your due date based on a first-trimester ultrasound (most reliable), the size of the gestational sac, or measurements like crown-rump length. If the ultrasound estimate differs from the LMP-based date by more than seven days, the ultrasound date is typically used.
Full-term is 37-42 weeks. Babies born before 37 weeks are preterm; between 37 and 38 weeks 6 days is early term; 39-40 weeks 6 days is full term; 41 weeks onward is late term; 42+ weeks is post-term. Healthy births happen across this entire range.