Pregnancy Due Date Calculator
Estimate your pregnancy due date from your last period, free and in your browser — with how many weeks along you are and your trimester.
Report a problemThis is an estimate based on a standard 40-week pregnancy. Only about 5% of babies arrive on their exact due date — treat it as a guide, not medical advice, and speak to your doctor or midwife.
How to use
- Pick the first day of your last menstrual period (the day your period started, not when it ended).
- If your cycle is longer or shorter than 28 days, type your average length — the estimate shifts to match. The result updates live as you change either box.
- Read your estimated due date, how many weeks and days along you are today, and which trimester that falls in.
FAQ
How is the due date calculated?
It uses Naegele's rule, the method midwives and doctors use: count 280 days (40 weeks) forward from the first day of your last menstrual period. If your average cycle is longer or shorter than 28 days, the estimate is nudged by the difference, because the date you ovulate shifts with your cycle. How far along you are is simply the number of days from your last period until today, shown as weeks and days, with the trimester worked out from the week count.
Is anything I enter sent to a server?
No. Your dates are used for plain arithmetic right in your browser — nothing is uploaded or stored. The calculator works offline and keeps your information private.
How accurate is a due date estimate?
It is only an estimate. A due date marks 40 weeks, but a healthy pregnancy can arrive any time from around 37 to 42 weeks, and only about 1 in 20 babies are born on the exact date. An early ultrasound usually gives a more precise date. This is a guide, not medical advice — your doctor or midwife is the best source for your pregnancy.