Pregnancy Due Date Calculator
Estimate your due date, trimester milestones and how far along you are.
How to use: Enter the first day of your last period (and your cycle length) to estimate the due date.
How to use the Pregnancy Due Date Calculator
Doctors date a pregnancy from the first day of the last menstrual period (LMP), not from conception. A full-term pregnancy lasts about 40 weeks, or 280 days, from that date. This calculator applies Naegele’s rule: it adds 280 days to your LMP and adjusts for your cycle length.
Enter the first day of your last period and your usual cycle length. If your cycle is longer or shorter than the typical 28 days, ovulation occurs later or earlier, and the due date shifts by the difference. The tool then shows your estimated due date, an approximate conception date, how many weeks and days pregnant you are today, and the dates when each trimester ends.
Keep in mind that only about 4% of babies are born on their exact due date. Most arrive between 37 and 42 weeks. Early ultrasound measurements are often used to confirm or correct dating, so your healthcare provider’s date takes priority over any calculator.
This page is for general information only and is not medical advice. If your cycles are irregular, you are unsure of your dates, or you have any concerns about your pregnancy, speak to a midwife or doctor. Nothing you enter leaves your device.
Frequently asked questions
How is the due date calculated?
By adding 280 days (40 weeks) to the first day of the last menstrual period, with an adjustment if the cycle is not 28 days.
How accurate is a due date?
It is an estimate. Only around 4% of babies are born on the due date, and most arrive within two weeks either side.
What if my cycles are irregular?
Dating by LMP is less reliable. An early ultrasound gives a more accurate estimate, so follow your provider’s dating.