Estimate a due date from the first day of the last menstrual period, with an optional adjustment for usual cycle length.
Calculate your estimate
Enter your details below. Required fields are marked by your browser.
How this calculator can help
The estimate can help prepare questions and milestones for prenatal care. It cannot confirm pregnancy or determine an official due date. A clinician may revise dating using ultrasound and other information.
How the estimate works
The standard estimate is 280 days after the first day of the last menstrual period. Because that convention assumes a 28-day cycle with ovulation near day 14, this tool optionally adjusts by the difference between the entered cycle length and 28 days.
Sources and methodology
We use transparent formulas and primary public-health or research sources. Calculators simplify real life, so their results should be interpreted as estimates.