Pregnancy Due Date Calculator
Calculate your baby’s due date from your last period or conception date, and see how many weeks pregnant you are and your trimester.
About the Pregnancy Due Date Calculator
The pregnancy due date calculator estimates when your baby is likely to arrive. It also tells you how far along you are, which trimester you are in and the key dates ahead. Only about 4% of babies are born exactly on their due date, so think of it as the middle of a two-week window.
How to Use the Pregnancy Due Date Calculator
- Choose whether you know the first day of your last period or the conception date.
- Enter the date and, for the period method, your usual cycle length.
- Press Calculate to see your due date and pregnancy progress.
Formula and How It Works
Naegele’s rule: due date = first day of last period + 280 days (40 weeks), adjusted by the difference between your cycle length and 28 days. From a known conception date, the due date is conception + 266 days.
Frequently Asked Questions
How accurate is a due date calculator?
It gives the same estimate your doctor starts with. An early ultrasound scan is more accurate and may change the date by a few days.
When does each trimester start?
The first trimester is weeks 1–13, the second is weeks 14–27 and the third is from week 28 until birth.
Results are estimates for general information and are not medical or veterinary advice. Please speak to a qualified professional about your own situation.