General tools
Due date calculator
Estimate a pregnancy due date from your last period, conception date, or IVF transfer, and see how far along you are today. Everything runs in your browser - nothing is uploaded.
A due date is an estimate - only about 1 baby in 20 arrives on it. Let your midwife or doctor confirm dating with a scan.
How it works
A pregnancy due date is an estimate of when a baby is likely to arrive, counted as 40 weeks from the first day of the last menstrual period (LMP). This calculator works that out for you with the standard Naegele's rule - LMP plus 280 days - and also lets you start from a known conception date (plus 266 days) or an IVF embryo transfer, where the embryo's age at transfer is subtracted so a day-5 blastocyst and a day-3 embryo both land on the right date.
Once you pick a method and a date, the tool shows the estimated due date along with how far along you are today, expressed the way clinicians do it: completed weeks plus days (for example 12 weeks and 3 days), and which trimester that falls in. Everything runs in your browser and nothing is sent to a server. Remember that a due date is an estimate - only about one baby in twenty actually arrives on it - so treat it as a guide and let your midwife or doctor confirm dating with a scan.
Example. If your last period started on 1 January 2026, Naegele's rule puts the due date at 8 October 2026. Switch to the conception method and enter a date about two weeks later and you get the same window; the IVF method asks for the transfer date and whether the embryo was day 3 or day 5.
FAQ
How is a due date calculated from the last period?
The common method, Naegele's rule, adds 280 days (40 weeks) to the first day of your last menstrual period. It assumes a regular 28-day cycle with ovulation around day 14, which is why a due date from an LMP is an estimate rather than an exact date.
What is the difference between the conception and LMP methods?
Conception happens about two weeks after the last period starts, so the conception method counts 266 days (38 weeks) from the conception date instead of 280 from the LMP. If you know the date of conception or ovulation, that method can be a little more precise; otherwise the LMP method is the usual starting point.
How does the IVF option work?
For IVF the tool counts forward from the embryo transfer date, adjusting for the embryo's age. It uses 266 days from conception and subtracts the embryo age at transfer, so a day-5 blastocyst is dated as transfer plus 261 days and a day-3 embryo as transfer plus 263 days.
How accurate is an estimated due date?
It is an estimate. Only around 5% of babies are born on their exact due date, and a full-term birth can happen any time from about 37 to 42 weeks. An early ultrasound is the most reliable way to date a pregnancy, so use this as a guide and confirm with your healthcare provider.