Pregnancy Calculator - Due Date, Weeks & Schedule

Already have a due date from your doctor or midwife? You can enter it here to work backwards. It's useful if you want to figure out how many weeks along you are today, or just want to map out your trimesters based on a date you've already been given.

Type in the due date and the calculator does the rest. It'll show you where you currently stand in your pregnancy and when the major milestones are coming up.

This is the most common starting point. Enter the first day of your last period and the calculator estimates your due date by adding 280 days (40 weeks) from there. It assumes a standard 28-day cycle by default, though many calculators let you adjust if yours runs longer or shorter.

Worth noting: this method counts from before you actually conceived, which is why pregnancy is technically considered to start before fertilization. It sounds a bit odd at first, but it's the standard way ob-gyns track gestational age and has been for a long time.

If you have a good sense of when you conceived, maybe you were tracking ovulation, using a predictor kit, or just have reason to be confident about the timing, enter that date here. The calculator adds 266 days (38 weeks) from conception to estimate your due date.

One thing to keep in mind: sperm can survive in the body for up to five days, so conception doesn't always line up exactly with the day of intercourse. The estimate will be close, but treat it as a reasonable approximation rather than a definitive answer.

A dating ultrasound is typically done between 8 and 13 weeks. It measures the baby's size to estimate gestational age. If you have a gestational age from an ultrasound report, enter that number along with the date the scan was done and the calculator works out your due date and current weeks from there.

Early ultrasounds are generally considered the most reliable way to date a pregnancy because they aren't thrown off by irregular cycles. If the ultrasound estimate differs from your LMP-based date by more than a week, your provider will usually go with the ultrasound reading.

IVF pregnancies get dated a little differently because the fertilization date is actually known. For a Day 5 embryo transfer (blastocyst), the calculator adds 261 days to the transfer date. For a Day 3 transfer, it adds 263 days. The difference accounts for the fact that the embryo was already a few days old at the time of transfer.

Since IVF timing is so precise, due dates calculated this way tend to be more accurate than LMP-based estimates. Your fertility clinic will probably give you an estimated due date at your transfer appointment, and this method should line up with it pretty closely.

Naegele's Rule has been used to estimate due dates for over 200 years and it's still the baseline today. The math is simple enough:

1. Take the first day of your last menstrual period.
2. Add one year.
3. Subtract three months.
4. Add seven days.

So if your LMP was July 10, you'd move to July 10 of the next year, subtract three months to land on April 10, then add seven days. That gives you an estimated due date of April 17.

The formula was built around a 28-day cycle with ovulation on day 14. If your cycle consistently runs longer or shorter than that, your ovulation date shifts, and so does your due date. Most modern calculators let you enter your average cycle length to adjust for this.

Honestly, it's an estimate. Only about 4% of babies actually arrive on their due date. Most come within a two-week window on either side. Anywhere between 39 and 40 weeks is considered full term, and 37 to 39 weeks is early term.

How accurate the date is depends a lot on how it was determined. An early ultrasound before 14 weeks is the most precise method, with a margin of error of roughly plus or minus 5 to 7 days. LMP-based estimates carry more uncertainty, especially if your cycles are irregular or you're not totally sure of the date.

Think of your due date as the center of a target, not a hard deadline. It gives you and your care team a shared reference point for when to expect labor and when to start paying closer attention.

These two terms sound interchangeable but they're not. Gestational age is counted from the first day of your last menstrual period. That's the standard in clinical settings. Fetal age (sometimes called embryonic age) counts from the actual day of conception, which is usually about two weeks later.

When your doctor says you're 10 weeks pregnant, they mean 10 weeks gestational age. The fetus itself is closer to 8 weeks old. The distinction mostly matters when you're reading ultrasound reports or looking at fetal development in medical literature, where fetal age sometimes shows up instead. For everyday tracking, gestational age is the number to follow.