Pregnancy Due Date Calculator
Enter the first day of your last period — get the estimated due date, how far along that is, and the current trimester.
Private by design: this tool runs entirely in your browser. Your files are never uploaded to a server, and nothing is stored.
Estimated due date: —
Not medical advice: this is a standard-formula estimate. Your doctor or midwife will date the pregnancy precisely — usually from an early ultrasound — and that date is the one that counts.
How to use it
Enter the first day of your last period. That's the date Naegele's rule starts from.
Get the estimate. Due date, weeks along, trimester, and the estimated conception date.
Confirm with your provider. An ultrasound in the first trimester dates a pregnancy most accurately.
Why 40 weeks — and why only ~4% arrive "on time"
Naegele's rule adds 280 days to the first day of the last period, on the assumption of a 28-day cycle with ovulation around day 14. It is the standard first estimate worldwide — and deliberately rough: only about 4–5% of babies arrive on their exact due date, with most coming within the two weeks before or after. Cycle length, implantation timing and simple memory of the last-period date all move the real number, which is why the first ultrasound usually refines it.