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Free tool · no sign-upEnter your last period, conception or IVF transfer date to find your estimated birth day and how many weeks along you are today.
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The most common method is Naegele’s rule: 280 days (40 weeks) are added to the first day of your last period. If you know the conception date, it is 266 days from fertilization; for an IVF pregnancy the calculation is based on the day the embryo was transferred. If your cycle isn’t 28 days, ovulation shifts, so the last-period method adjusts accordingly.
The date you get is an estimate — not a deadline. Pregnancies usually end between weeks 37 and 42, and every baby has its own timing. The estimated date is a starting point for planning your check-ups and following development week by week.
How is a due date calculated?
The most common method adds 40 weeks (280 days) to your last period — this is Naegele’s rule. If you know the conception date it is 266 days, and for IVF it is based on the embryo’s age.
Is the estimated due date exact?
No, it is an estimate. Only a small share of babies arrive on the exact date; most are born between weeks 37 and 42. The most accurate date comes from an early-pregnancy ultrasound.
How is an IVF due date found?
The embryo’s age is subtracted from the transfer date: for a 5-day blastocyst transfer the date is transfer + 261 days, and for a 3-day embryo transfer + 263 days. The date your doctor gave you takes priority.
What if my periods are irregular?
The last-period method is less reliable with irregular cycles. Entering your cycle length helps; still, an ultrasound gives the most accurate result — ask your doctor.
This calculation is based on Naegele’s rule (last period + 280 days) and on ACOG / FIGO 2018 criteria. The result is an estimate and doesn’t replace medical advice; the exact date is confirmed by an early-pregnancy ultrasound. If anything worries you, talk to your doctor.
Other tools: Pregnancy calculator · Ovulation calculator · Period calendar