Pregnancy Due Date Calculator

Start from the first day of your last period, then adjust for your actual average cycle length instead of assuming 28 days. Every day your cycle runs longer than 28 pushes ovulation — and your due date — later; every day shorter moves it earlier. This calculator’s cycle-length slider makes that adjustment automatically. If your cycles are very irregular, a dating ultrasound will usually be more reliable than any LMP-based estimate.

For a Day 5 blastocyst transfer, add 261 days to the transfer date. This comes from the standard 266-day conception-to-birth interval, minus the 5 days the embryo already spent developing before transfer. A Day 3 transfer instead adds 263 days, and a Day 6 transfer adds 260 days.

Most standard due dates are calculated from the last menstrual period (LMP) using Naegele’s rule — LMP plus 280 days — because the LMP date is usually known, while the exact conception date often is not. When conception date is known precisely, such as with IVF or careful ovulation tracking, providers instead add 266 days from conception, which typically lands on nearly the same date.

Yes. A first-trimester ultrasound is considered the most accurate single dating method, because early fetal measurements are very consistent between pregnancies. If your scan-based gestational age disagrees with your LMP-based estimate by more than roughly 5–7 days in the first trimester (with wider allowances later in pregnancy), many providers will re-date the pregnancy using the ultrasound instead.

Enter your last period, conception date, IVF transfer date, or ultrasound information above, and the calculator shows your current gestational age in weeks and days, updated to today’s date automatically.

Pregnancy is commonly divided into three trimesters: the first runs from week 1 through the end of week 13, the second from week 14 through the end of week 27, and the third from week 28 until birth, typically around week 40. The ribbon visual above marks exactly where you currently fall on that timeline.

Due date calculators give a statistically well-founded estimate, not a guarantee. Only a small percentage of babies are born on their exact estimated due date; most arrive within about two weeks before or after it. Accuracy depends heavily on the dating method — ultrasound and IVF-based dating tend to be tighter than LMP-based estimates for someone with irregular cycles.

Naegele’s rule is the traditional formula for estimating a due date: take the first day of the last menstrual period, add one year, subtract three months, and add seven days — which is mathematically the same as simply adding 280 days. It assumes a 28-day cycle with ovulation on day 14.

No. The formula only depends on the embryo’s developmental age at transfer (Day 3, 5, or 6), not on whether the cycle was fresh or frozen (FET). A frozen Day 5 blastocyst is still treated as 5 days old on the day it is transferred.

A pregnancy is generally considered full term between 39 weeks 0 days and 40 weeks 6 days. Babies born from 37 weeks 0 days through 38 weeks 6 days are called early term, and those born at or after 41 weeks are considered late or post-term — each category carries slightly different clinical guidance.

If your last period date is uncertain, the conception, IVF, or ultrasound tabs will generally give you a more dependable estimate than the LMP method. For any pregnancy following a recent loss, a dating ultrasound with your care provider is the most reliable way to confirm gestational age.

Because the embryo has already been developing for several days before transfer, it is older than a newly fertilized egg on that date. Subtracting the embryo’s age from the standard 266-day post-conception interval keeps the gestational-age math aligned with how a natural pregnancy would be dated at the same developmental stage.