What is Pregnancy Due Date Calculator?

Pregnancy Due Date Calculator estimates your expected delivery date from your last period, conception date, IVF transfer, ultrasound scan, or a due date you already have on hand. It returns the estimated date of delivery, the full-term safe birth window (37 to 42 weeks), trimester milestones, and adjusted due dates for twins and triplets.

The estimated date of delivery (EDD) follows Naegele's rule: 280 days from the first day of the last menstrual period, adjusted for cycle length when needed. Five calculation modes cover the common starting points: last period (LMP), conception date, IVF transfer (day 3 or day 5), an ultrasound scan with the gestational age the sonographer reported, and a reverse mode that back-derives everything from a due date your doctor already gave you. Every result includes the current week and day, days remaining, the boundary dates for each trimester, a safe birth window covering weeks 37 through 42, and adjusted due dates for twin and triplet pregnancies.

How to use

1. Step 1 — Pick a calculation mode: Last Period, Conception Date, IVF Transfer, Ultrasound, or Known Due Date.
2. Step 2 — Enter the date that mode asks for. The tool returns your due date, the safe birth window, and the multiples-adjusted dates instantly.
3. Step 3 — Review the trimester timeline, weekly progress, and milestone dates. Copy the full summary to share with a partner or doctor.

When to use

• Quickly check the due date after a positive home pregnancy test.
• Plan maternity leave by working out which trimester each week falls into.
• Confirm the trimester boundary before your 12-week or 20-week scan.

Result

Your last period started on January 15, 2026. The calculator estimates your due date as October 22, 2026 and shows you are currently in week 8 of your first trimester.

FAQ

How accurate is a due date calculated from the LMP?

Naegele's rule is the obstetric standard, but only about 4% of babies actually arrive on the exact due date. A two-week window either side of the EDD is considered normal-term delivery.

What if I don't remember the first day of my last period?

Switch to Ultrasound mode if you have had a dating scan — it uses the gestational age the sonographer measured and is far more accurate than period-based math. Conception Date or IVF Transfer modes are also good fallbacks if you remember either event.

Why does the calculator block dates more than 40 weeks ago?

A standard human pregnancy lasts about 40 weeks. If the LMP you enter is older than that, the math suggests the baby was already born, so the result wouldn't be meaningful as a due date estimate.

When does each trimester start and end?

The first trimester runs from week 1 to the end of week 12, the second from week 13 to the end of week 27, and the third from week 28 until birth. The calculator shows the exact calendar dates of those switches.

Is the calculation different for IVF pregnancies?

Yes. For IVF, the due date is based on the embryo transfer date, not the LMP. If you're in an IVF cycle, ask your clinic for the exact EDD they recorded — it won't match this LMP-based calculation.

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