What we do
Our main tool, the Due Date Calculator, estimates a pregnancy due date using the same standard methods used in prenatal care: Naegele’s rule from the last menstrual period, 266 days from conception, and embryo-age-adjusted dating for IVF. Our second main tool, the Date Calculator, counts the days between dates and adds or subtracts days, weeks, months and years.
How we keep calculations accurate
All calculations use whole calendar days on the Gregorian calendar, so leap years and month lengths are always handled. Every formula is shown on the page so you can check the result yourself, and the calculators are covered by automated tests for edge cases such as February 29, month ends and dates in reverse order.
Privacy
The calculators run in your browser. The dates you enter are not stored. See our Privacy Policy for details.
Medical information
Pregnancy results are estimates for general information. They do not replace advice from a doctor, midwife or other healthcare professional. Please read our Medical Disclaimer.