Due Date Calculator
Free pregnancy due date calculator: your estimated due date, conception date and current week by Naegele's rule, from your last period. In-browser.
updated
- ✓ Runs in your browser — nothing uploaded
- ✓ No sign-up
- ✓ Free, no limits
This due date calculator estimates when your baby will arrive from the first day of your last menstrual period (LMP). Pick the date, set your average cycle length, and it returns the estimated due date, the likely conception date, and how far along you are today — weeks plus days, with the trimester.
It uses Naegele's rule, the same arithmetic printed in obstetric textbooks: due date = LMP plus 280 days, adjusted by a day for every day your cycle differs from 28. Worked example: an LMP of 1 January with a 28-day cycle gives a due date of 8 October; a 30-day cycle moves it to 10 October. Conception is placed at ovulation, about 14 days before the next period would have started.
An honest note on precision: only around 4–5% of babies arrive on their due date — it is the middle of a distribution, and most arrive within two weeks either side. A first-trimester dating scan outranks any calendar rule, so treat this as orientation between appointments, not a verdict. Your dates never leave your browser — nothing here is uploaded or stored.
Frequently asked questions
How is a due date calculated?
Naegele's rule: 280 days (40 weeks) after the first day of your last period, shifted by a day for each day your cycle differs from 28. Ultrasound dating in the first trimester is more accurate and replaces the calendar estimate when they disagree.
How accurate is the due date?
It is a midpoint, not a promise: roughly 4–5% of babies arrive on the exact date, and most come within two weeks either side. 'Full term' itself spans weeks 39–40.
What if my cycles are irregular?
Calendar rules assume a steady cycle, so an irregular one makes the LMP estimate rough. Use your best average here, and rely on the dating scan — it measures the embryo directly and doesn't care about your calendar.
Is anything I enter stored?
No. The dates are computed in your browser and never uploaded — there is no server behind this page.