Pregnancy Due Date Calculator
Enter the first day of your last period, or another known date, to estimate your due date, how far along you are, and when each trimester ends.
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This is an estimate based on standard formulas, not medical advice. Only about 1 in 20 babies arrive exactly on their due date; your doctor or midwife may adjust it after an ultrasound.
How to Use
- 1Choose what you know: last period, conception date, or IVF transfer date.
- 2Pick the date. For last-period dating, adjust your usual cycle length if it isn't 28 days.
- 3See your estimated due date, current week and day, and trimester.
- 4Check the milestone dates, such as the end of each trimester and full term.
Frequently Asked Questions
How is the due date calculated?
The standard method (Naegele's rule) adds 280 days, or 40 weeks, to the first day of your last menstrual period. If your cycle is longer or shorter than 28 days, the date shifts by the difference. From a known conception date it adds 266 days, and for IVF it counts from the transfer date and the embryo's age.
Why does pregnancy count from my last period, not conception?
The date of the last period is usually known, while the exact day of conception rarely is. So by convention, pregnancy weeks start about two weeks before conception actually happens.
Can the due date change?
Yes. An early ultrasound, usually in the first trimester, measures the baby and is often used to confirm or adjust the date. Always follow the date your healthcare provider gives you.
Is my information stored?
No. The calculation happens in your browser and nothing you enter is saved or sent anywhere.