Estimate your baby's due date from your last period
💡 Why This Matters Knowing your estimated due date helps you track pregnancy milestones, plan for appointments, and know roughly when to expect your baby — based on the standard method doctors use first.
Naegele's rule is named after a German obstetrician who published it in 1812 — over 200 years later, it's still the default starting point doctors use before any ultrasound is done.
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This calculator uses Naegele's rule, the standard method doctors use for an initial due date estimate. It takes the first day of your last menstrual period (LMP), adds one year, subtracts three months, and adds seven days — assuming a typical 28-day cycle with ovulation around day 14.
The date you get is an estimate of a full-term (40-week) pregnancy counted from your LMP, not from conception. It's the same starting point your doctor will likely use at your first appointment, before any ultrasound dating adjusts it.
Naegele's rule assumes a standard 28-day cycle with ovulation on day 14 — if your cycle runs longer, shorter, or irregular, your real due date could shift by a week or more. It also doesn't account for the ~5% of pregnancies that naturally go past 40 weeks or arrive early.
Use this as a planning starting point — for tracking milestones, scheduling appointments, and general preparation. Your doctor will likely confirm or adjust the date using an early ultrasound, which is generally considered more precise than LMP-based dating alone.
Example: Say your last period started on January 10, 2026. Add one year → January 10, 2027. Subtract three months → October 10, 2026. Add seven days → your estimated due date is October 17, 2026.
Only about 1 in 20 babies arrive on their exact due date. Naegele's rule gives a useful target, but a full-term birth anywhere within about two weeks either side is completely normal.
This calculator assumes a standard 28-day cycle. If your cycles run longer or shorter, your actual conception date — and due date — may shift earlier or later than the estimate.
Not necessarily. Ultrasound dating measures fetal size directly and is often considered more precise, especially if your cycle is irregular. Your doctor may adjust the date based on ultrasound findings.