Pregnancy Due Date Calculator
Estimate your due date and current gestational age from your last period or conception date.
Assumptions used in this calculation
- Cycle assumption: Naegele's rule assumes a regular 28-day cycle with ovulation on day 14; actual timing varies by individual.Naegele's rule
About this calculator
Counting forward 40 weeks from a single date by hand, and then also figuring out how many weeks pregnant you currently are, means keeping track of two separate date calculations across changing calendar months, easy to get off by a few days. This calculator applies Naegele's rule, the standard obstetric estimate, to compute an estimated due date from either the first day of your last menstrual period (adding 280 days) or a known conception date (adding 266 days), and it simultaneously calculates your current gestational age in weeks and days along with which trimester you're in. Because it does both calculations from a single date entry, you get the due date and your current pregnancy stage together rather than working them out separately. Naegele's rule assumes a standard 28-day cycle with ovulation on day 14, so it's a population-based estimate: only around 5% of babies are actually born on their calculated due date, with most arriving within roughly two weeks either side.
Worked example
Last period: Jan 1, 2026
Result: Estimated due date: October 8, 2026
Was this helpful?