Due Date Calculator — pregnancy estimator
Estimate your due date from your last period or conception date, with gestational age and trimester — in your browser.
🔒 Runs entirely in your browser. Your input and output are never sent to a server or stored — fully private.
Estimate your due date from your last menstrual period (LMP) or a known conception date.
⚠️ An estimate only — not medical advice. Consult your doctor or midwife.
About this tool
Expecting and want a rough timeline? Enter the first day of your last menstrual period and this calculator applies Naegele's rule — that date plus 280 days — to estimate your due date, or you can work from a known conception date instead. It also shows how many weeks and days pregnant you are right now, along with the trimester. It is a quick way to plan appointments and milestones. Every date is worked out in your browser, so nothing you enter is uploaded or stored.
Frequently asked questions
How is the due date calculated?
By default it uses Naegele's rule: it takes the first day of your last menstrual period and adds 280 days, which is 40 weeks. This assumes a regular 28-day cycle with ovulation around day 14. If you choose the conception-date option instead, it counts 266 days from that day, since fertilisation happens about two weeks after the period starts. Both land on the same estimate for a textbook cycle.
Will my baby arrive on the due date?
Probably not on the exact day. A due date is a single midpoint, and only around one in twenty babies actually arrives on it. A pregnancy is considered full term anywhere from 37 to 42 weeks, so a healthy birth a couple of weeks either side is completely normal. Treat the date as the centre of a window rather than a deadline, and let your care team track how things progress.
Is this a substitute for a doctor's dating scan?
No. This is a general estimate for your own planning, not medical advice or a diagnosis. Cycle length, irregular periods and other factors can shift the real dates, and an early ultrasound usually gives a more accurate result. Always confirm your due date and any concerns with a doctor or midwife. The whole calculation runs locally in your browser, so the dates you enter are never uploaded or stored.