Health
Your estimated due date and current week of pregnancy, based on your last menstrual period.
Estimated due date
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Enter the first day of your last period
Estimated using Naegele's rule (280 days from your last period) — a standard estimate, not a diagnosis. Actual due dates vary; your doctor's ultrasound-based estimate is more accurate.
If the first day of your last period was March 1, adding 280 days (Naegele's rule) lands the estimated due date on December 5 — about 40 weeks later. If today's date is, say, June 15, the calculator also shows you're currently about 15 weeks pregnant, calculated from the same starting date.
Naegele's rule assumes a standard 28-day cycle with ovulation on day 14 — actual cycle length varies significantly between people, which is why only a small percentage of babies arrive exactly on their calculated due date. An early ultrasound typically gives a more precise estimate, especially for irregular cycles, so treat this figure as a planning reference rather than a fixed date.
Using Naegele's rule — adding 280 days (40 weeks) to the first day of your last menstrual period. It's a standard estimate used widely in obstetrics, though only a small percentage of babies arrive exactly on their estimated due date.
The calculator shows this automatically based on the number of days since your last period, once you enter the date.
It's a reasonable starting estimate, but an early ultrasound is generally considered more accurate for confirming gestational age, especially if your cycle is irregular.