Due Date Calculator

How your due date is calculated

The standard estimate is Naegele's rule: a pregnancy is counted as 280 days (40 weeks) from the first day of your last menstrual period (LMP) — not from conception. It's counted this way because the LMP is a date most people can pinpoint, while the exact day of conception usually isn't known. This calculator adds 280 days to your LMP and adjusts for your cycle length.

Why cycle length matters

The 280-day rule assumes a textbook 28-day cycle with ovulation around day 14. If your cycles run longer or shorter, you likely ovulate earlier or later, which shifts the due date. A 32-day cycle, for example, pushes the estimate about four days later. Entering your real average cycle length makes the estimate a little more personal.

The three trimesters

• First trimester: weeks 1–13 — the embryo develops into a fetus; early symptoms are common.
• Second trimester: weeks 14–27 — often the most comfortable stretch; movement begins.
• Third trimester: weeks 28–40 — rapid growth and final preparation for birth.

"How far along" is shown in weeks and days (e.g. 24w 3d), the same way clinicians describe gestational age.

FAQ

How accurate is a due date?

It's an estimate, not an appointment. Only about 1 in 20 babies arrive on the exact due date; most are born within two weeks either side. An early ultrasound (especially in the first trimester) is the most accurate way to date a pregnancy and may revise this estimate.

I know my conception date — can I use that?

Conception is roughly two weeks after the LMP in a 28-day cycle, so add about 266 days to a known conception date instead. This tool is built around the LMP, which is the clinical standard.

Does adjusting my cycle length change the due date?

Yes. The 280-day rule assumes a 28-day cycle, so if yours is longer or shorter the tool shifts the estimate to reflect when you likely ovulate. A 32-day cycle, for instance, moves the due date about four days later than the textbook calculation.

Can it tell me how far along I am right now?

Yes. Alongside the due date it shows your current gestational age in weeks and days (for example 24w 3d) and which trimester you're in, the same way clinicians describe a pregnancy.

Does my information stay private?

Yes. The dates you enter are processed entirely in your browser and are never uploaded or stored, so your pregnancy information stays on your device.

Is the due date calculator free?

Yes, it's free with no sign-up and works on phones and desktops. It's for general information only, not a substitute for prenatal care.

This tool is for general information only and isn't medical advice. Confirm any pregnancy dating with your healthcare provider.