Pregnancy Due Date Calculator
Estimate your due date
This free Pregnancy Due Date Calculator estimates when your baby is likely to arrive, based on the first day of your last menstrual period. It follows the standard method used in clinics: a pregnancy is dated as lasting about 280 days, or forty weeks, from that first day, and the total is adjusted if your usual cycle is longer or shorter than the typical twenty eight days. Along with the due date, the tool shows how far along you are today in weeks and days, which trimester you are in, and the calendar dates when the second and third trimesters begin.
Please remember this is an estimate only, not medical advice, and it is not a substitute for care from your doctor or midwife. Only a small minority of babies arrive on their exact due date; most are born somewhere in the surrounding few weeks, and an early ultrasound scan usually dates a pregnancy more precisely than period dates, especially if cycles are irregular. Your care provider may adjust your official due date after a scan, and their date is the one to follow for appointments and decisions. Nothing you enter here is uploaded or stored — the calculation happens entirely in your browser.
How to use
- Enter the first day of your last menstrual period.
- Adjust the cycle length if yours is usually not twenty eight days.
- Click Calculate due date to see your estimated delivery date.
- Read how many weeks and days pregnant you are today.
- Note the trimester start dates for planning appointments and milestones.
Frequently asked questions
Why is pregnancy counted from the last period?
Ovulation and conception dates are hard to pin down, but the first day of the last period is a date most people can identify. Medicine therefore counts forty weeks from there, which means the first two counted weeks happen before conception even occurs.
How does cycle length change the due date?
The standard 280 days assumes ovulation on day fourteen of a twenty eight day cycle. A longer cycle usually means later ovulation, so the due date moves later by the difference; a shorter cycle moves it earlier, and the calculator applies that adjustment automatically.
How accurate is this estimate?
Roughly speaking it is a well-informed guide, not a prediction. Only about one baby in twenty arrives on the exact due date, while the large majority arrive within two weeks either side. A dating ultrasound in the first trimester is considered the most reliable way to set the date.
What if my periods are irregular?
Then period-based dating can be off by a week or more, because ovulation timing varies. Mention it at your first appointment; your provider will usually rely on an early scan measurement instead, and that date should be the one you plan around.