Pregnancy Due Date Calculator
Your estimated due date from your last period.
Enter the first day of your last menstrual period (LMP) to estimate your due date using Naegele's rule — the same 40-week method clinicians start with. Only about 5% of babies arrive on their due date, so treat it as a planning landmark, and confirm everything with your healthcare provider.
How it's calculated
Naegele's rule: estimated due date = first day of LMP + 280 days (40 weeks). If you enter today's date, it also reports current gestation in weeks and days.
Frequently asked questions
How accurate is the due date?
It's an estimate: only around 5% of babies are born on their due date, and most arrive within two weeks either side. A first-trimester ultrasound gives a more precise dating than LMP alone.
Why 40 weeks from the last period?
Pregnancy is dated from the LMP because it's a date most people know; ovulation and conception typically happen about two weeks later. So at '4 weeks pregnant' the embryo is really about two weeks old.
What if my cycles are irregular?
Naegele's rule assumes a 28-day cycle with ovulation on day 14. With irregular or much longer cycles, the estimate shifts — an early ultrasound is the reliable way to date the pregnancy.