Due Date Calculator
Your due date, your week, and how big the baby is right now.
Estimate only — this is not medical advice. Always confirm dates with your doctor or midwife.
More fun, still free
How the due date calculator works
This free pregnancy calculator uses Naegele's rule: your estimated due date is 280 days (40 weeks) after the first day of your last menstrual period, or 266 days (38 weeks) after conception. It also shows your current pregnancy week, trimester, a weekly fruit size comparison and how many days are left. Switch modes to work backwards from a birth date and estimate when conception happened.
Frequently asked questions
How is a due date calculated?
Naegele's rule adds 280 days (40 weeks) to the first day of your last menstrual period, assuming a regular 28-day cycle. From a known conception date, the due date is 266 days (38 weeks) later.
How accurate is a due date calculator?
It is an estimate. Only about 4% of babies are born exactly on their due date, and most arrive within two weeks either side. An early ultrasound gives a more precise date.
What if my cycle is not 28 days?
Longer or shorter cycles shift ovulation, so the estimate moves by the same number of days. If your cycle is 32 days, add about 4 days to the calculated due date.
Can it tell me when conception happened?
Yes. In the second mode, enter a birth date and the calculator subtracts 266 days to show the most likely conception date plus a five-day window on each side.