Estimate a due date and see how far along a pregnancy is. Choose the method that fits the information you have: last menstrual period, conception date, IVF transfer date, or a dating ultrasound.
Choose a method and enter your dates.
This tool gives an estimate only and is not medical advice. An estimated due date is a guide, not a fixed date. Confirm your dates and your care with a qualified healthcare provider.
An estimated due date is a guide. Only about 1 in 20 babies arrives on the exact date.
About this calculator
A full-term pregnancy is counted as 280 days, or 40 weeks, measured from the first day of the last menstrual period. Working a due date out this way is known as Naegele's rule. The last-period method assumes ovulation around day 14 of a 28-day cycle, so this calculator adjusts the estimate when a different cycle length is entered. The conception method counts 266 days from conception. The IVF method counts from the transfer date, using 261 days for a day-5 blastocyst transfer and 263 days for a day-3 transfer. An ultrasound estimate uses the gestational age measured at the scan, which is often the most reliable method in early pregnancy.
This is an estimate and not medical advice. A due date marks the middle of a normal range, and a healthy birth commonly happens in the weeks around it rather than on the day itself. Dating scans, the health of the pregnancy and many other factors can change the picture, so any estimate here should be confirmed with a midwife or doctor. For background on how pregnancy is dated, the American College of Obstetricians and Gynecologists explains the standard methods.
Frequently asked questions
How is a due date calculated?
The most common method counts 280 days, which is 40 weeks, from the first day of the last menstrual period. This is called Naegele's rule. It assumes ovulation around two weeks into the cycle, so this calculator adjusts the result if the cycle is shorter or longer than 28 days. The conception, IVF transfer and ultrasound methods count from a different starting point but aim at the same 40-week full term.
How accurate is an estimated due date?
It is an estimate, not a fixed appointment. Studies consistently find that only a small share of babies, around 1 in 20, are born on their estimated due date. Most arrive in the surrounding weeks. A pregnancy is generally considered full term from 37 weeks. An early dating ultrasound is usually the most reliable estimate, and a healthcare provider may adjust the date after a scan.
What is the difference between the last-period and conception methods?
Pregnancy is normally dated from the first day of the last menstrual period, which is about two weeks before conception actually happens. That is why the last-period method uses 280 days and the conception method uses 266. If you know the conception date, for example from ovulation tracking, the conception method can be more direct. If you only know the last period, use that method and enter the usual cycle length.
How does an IVF transfer date change the calculation?
With IVF the timing is known precisely, so the due date is counted from the transfer. The embryo's age at transfer matters. A day-5 transfer uses a blastocyst, so the due date is 261 days after the transfer. A day-3 transfer is two days earlier in embryo development, so it is 263 days after the transfer. Choosing the right transfer type keeps the estimate accurate.
Is this calculator medical advice?
No. This tool gives a general estimate using standard dating methods, and it is not a substitute for professional care. A due date should be confirmed by a midwife or doctor, usually with a dating ultrasound. If you have any questions about a pregnancy or about your dates, speak to a qualified healthcare provider.