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A pregnancy due date calculator estimates when your baby is likely to arrive based on the first day of your last menstrual period, using the same method most doctors use at your first prenatal visit. It also shows how many weeks along you currently are and breaks down your pregnancy into trimesters, so you have a clear timeline from early on.
Everyone asks 'when am I due' the moment they find out they're pregnant, and doctors typically won't confirm this until your first scan weeks later. This tool exists to give an immediate estimate you can work with in the meantime, using the standard 280-day method from your last period.
The standard method adds 280 days (40 weeks) to the first day of your last period, which assumes a fairly typical 28-day cycle with ovulation around day 14. If your cycles run longer or shorter, the calculator adjusts the estimate accordingly. Keep in mind this is still an estimate — only about 5% of babies actually arrive exactly on their calculated due date, with most arriving within a week or two either side.
It gives a reasonable estimate, but only a small percentage of babies are born exactly on the calculated date — most arrive within a couple of weeks of it.
It's based on Naegele's rule, adding 280 days to the first day of your last menstrual period.
If you know your conception date or have an ultrasound estimate, that will generally give a more accurate result than this calculator alone.
Yes, longer or shorter cycles shift the estimated ovulation and conception date, which this calculator accounts for when you adjust cycle length.
The first trimester runs through week 13, the second through week 27, and the third continues until delivery around week 40.