Estimate your due date from the first day of your last period — plus how far along you are today and when each trimester ends.
Uses Naegele's rule (280 days from the last period) adjusted for cycle length. Only about 1 in 20 babies arrive on the exact due date; an ultrasound dating scan is more precise. Not medical advice — confirm with your provider.
The standard method (Naegele's rule) counts 280 days — 40 weeks — from the first day of your last menstrual period. If your cycle runs longer or shorter than 28 days, the estimate shifts by the difference, since ovulation moves with cycle length.
Due date ≈ last period + 280 days (± cycle-length adjustment)
It's an estimate — most births happen within about two weeks either side. A first-trimester ultrasound gives a more precise date.
Enter your average cycle length and the estimate adjusts, because a longer cycle usually means later ovulation and a later due date.
Related: ovulation calculator · age calculator · date difference calculator · all free calculators.
Yes. The Due Date Calculator is completely free, runs in your browser, and never asks for a signup, email, or download. Enter your numbers and the result updates instantly.
It uses standard formulas and recalculates the moment you change a value, so the math is exact for the inputs you enter. Treat the result as a reliable planning estimate; for decisions with legal or tax consequences, confirm the figures with a qualified professional.
Yes. The calculator is mobile-friendly and works on any phone, tablet, or computer — there is no app to install and nothing to save.
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Last reviewed: September 2026. Free to use, no signup — Due Date Calculator by ToolWise Digital.
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