Pregnancy Due Date Calculator
Estimate your due date from your last period.
Free · No sign-up · Works in your browser
About the Pregnancy Due Date Calculator
Estimate your baby's due date free — enter the first day of your last menstrual period (and your cycle length if it isn't 28 days) and get your estimated due date using Naegele's rule, the same LMP + 280 days method clinicians start from. You'll also see how many weeks pregnant you are today and when the second and third trimesters begin. Remember: it's an estimate — only about 1 in 20 babies arrives on the exact due date, and your provider's ultrasound dating takes precedence.
How to use the Pregnancy Due Date Calculator
- 1Enter the first day of your last period (LMP).
- 2Adjust your average cycle length if it isn't 28 days.
- 3Read your estimated due date, current week, and trimester dates.
Frequently asked questions
How is a due date calculated?
Naegele's rule: first day of the last menstrual period + 280 days (40 weeks), adjusted for cycle length. Ultrasound dating in the first trimester is the most accurate method.
How accurate are due dates?
Only about 4–5% of babies arrive on their exact due date; most are born within two weeks either side. Treat it as the middle of a window.
How many weeks pregnant am I?
Pregnancy is counted from the LMP, not conception — enter your LMP above and the calculator shows your current gestational age in weeks and days.