Enter the dates
Estimated due date
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About this tool
A due date is commonly estimated with Naegele's rule from the first day of the last menstrual period. This tool derives the due date from that date (and cycle length) and shows the pregnancy week at the reference date plus the trimester.
How weeks are counted
Pregnancy weeks are counted with the first day of the last period as "week 0, day 0". Ovulation and conception happen about two weeks later, but by convention the due date is "week 40, day 0" = last period + 280 days.
An estimate only
Actual delivery varies around the due date. With irregular cycles or a shifted ovulation day, this estimate will differ. The accurate due date and pregnancy progress are determined by a medical provider using ultrasound and other findings. Always follow your obstetric care.
Frequently asked questions
How is the due date calculated?+
Using Naegele's rule, 280 days (40 weeks) are added to the first day of the last menstrual period.
If the cycle differs from 28 days, it is adjusted by the difference. It is a general estimate.
If the cycle differs from 28 days, it is adjusted by the difference. It is a general estimate.
When does pregnancy week counting start?+
The first day of the last menstrual period is counted as week 0, day 0.
Actual ovulation and conception occur about two weeks later, but weeks are conventionally counted from this point.
Actual ovulation and conception occur about two weeks later, but weeks are conventionally counted from this point.
What if my cycle is not 28 days?+
Enter your cycle length and the due date is adjusted by the difference from 28 days.
A longer cycle shifts it later, a shorter one earlier. Still an estimate.
A longer cycle shifts it later, a shorter one earlier. Still an estimate.
How accurate is the due date?+
It is only an estimate. Actual delivery often varies, and the accurate due date is determined by a medical provider using ultrasound and other findings.
Always follow your doctor.
Always follow your doctor.
Are my inputs stored?+
No. All calculation happens in your browser, and the values you enter are never sent to or stored on a server.
Method & notes
・Due date = last menstrual period + 280 days (40 weeks), adjusted by (cycle − 28)
・Pregnancy week = (reference − last period) / 7 (weeks and days), counting the last period as week 0
・Trimesters (general): first ≤ 13w6d / second 14–27w6d / third from 28w
・A general calculation based on Naegele's rule; individual variation applies and medical diagnosis takes precedence.
・Due date = last menstrual period + 280 days (40 weeks), adjusted by (cycle − 28)
・Pregnancy week = (reference − last period) / 7 (weeks and days), counting the last period as week 0
・Trimesters (general): first ≤ 13w6d / second 14–27w6d / third from 28w
・A general calculation based on Naegele's rule; individual variation applies and medical diagnosis takes precedence.
Please note (important)
This site does not represent any medical institution and does not guarantee the accuracy of the results. The due date and pregnancy week here are a general estimate and may differ from reality. For the actual due date, pregnancy progress and health management, always follow the diagnosis of a doctor or medical institution.
This site does not represent any medical institution and does not guarantee the accuracy of the results. The due date and pregnancy week here are a general estimate and may differ from reality. For the actual due date, pregnancy progress and health management, always follow the diagnosis of a doctor or medical institution.