This due date calculator estimates when your baby is due and shows which week of pregnancy you are in today. It is based on the first day of your last period and your usual cycle length.
How the due date is calculated
The calculator uses Naegele’s rule, the standard method in obstetrics: 280 days (40 weeks) are added to the first day of the last period. If your cycle is longer or shorter than 28 days, the date is shifted by the difference, because ovulation shifts accordingly.
How weeks of pregnancy are counted
Pregnancy is counted from the first day of the last period – about two weeks before conception. “12+3” means 12 completed weeks and 3 days. A birth between 37+0 and 41+6 weeks is considered term.
How accurate is the due date?
Only a small share of babies are born on their due date. It is a point of reference. If your cycle is irregular or you do not know when your last period started, the calculation is unreliable. During prenatal care the date is therefore checked by an ultrasound scan in the first trimester and corrected if needed.
Frequently asked questions
What if I don’t know when my last period started?
Then the due date cannot be calculated reliably. Your doctor or midwife will determine the stage of pregnancy by ultrasound.
Why did my doctor give me a different date?
An ultrasound scan in the first trimester is more accurate than calculating from the last period. If the two differ clearly, the ultrasound date usually applies.
When is a baby considered premature?
A birth before 37+0 weeks of pregnancy is called a preterm birth.
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Note: This calculator provides general information and does not replace prenatal care. Your entries are not stored.