Pregnancy Due Date Calculator

Estimate your baby’s due date from the first day of your last menstrual period. One of the first questions after a positive test is “when is it due?” — and the answer shapes every antenatal appointment that follows. Using Naegele’s rule (LMP + 280 days), the calculator also tells you how many weeks pregnant you are right now.

First day of last menstrual period

How to Use the Pregnancy Due Date Calculator

Pick the first day of your last menstrual period from the date picker — not the day it ended.
Press Calculate.
See your estimated due date and your current week of pregnancy.
Use the week count to follow along with week-by-week pregnancy guides and schedule checkups.

Practical example

If your last period started on 1 January 2026, your estimated due date is 8 October 2026 — 280 days later. If today is 100 days after that date, you are 14 weeks and 2 days pregnant, well into the second trimester, which is typically when the anatomy scan is scheduled. If the dates put you past 42 weeks, the tool flags it so you can contact your doctor promptly rather than waiting.

Key features and benefits

Naegele’s rule: the standard 280-day method used by doctors worldwide.
Current week: automatically works out how far along you are, in weeks and days.
Past-term flag: warns if the dates suggest a post-term pregnancy needing medical attention.
Future-date guard: catches accidental future dates with a friendly message.
Private: sensitive dates never leave your browser.

Limitations

This assumes a regular 28-day cycle with ovulation on day 14 — real cycles vary widely, and irregular cycles make LMP-based dating unreliable. Only about 5% of babies arrive on their due date; most come within two weeks either side. A dating ultrasound, especially in the first trimester, gives a far more accurate estimate. Always confirm with your doctor or midwife, and never use this tool to make medical decisions alone. If you are unsure of your LMP date, an early ultrasound can establish dating — and once that scan date is set, it generally takes precedence over LMP-based calculations for the rest of the pregnancy.