Due date calculator
Enter the first day of your last period to estimate your due date and how far along you are. Private — it runs in your browser, and nothing is saved.
How it works
Your estimated due date is the first day of your last menstrual period (LMP) plus 280 days (40 weeks) — the standard clinical method, Naegele’s rule. Because ovulation usually happens about 14 days before your next period, we adjust the estimate by any difference between your cycle length and 28 days, so a longer or shorter cycle shifts the date accordingly.
This is an estimate, not a diagnosis. An early ultrasound dating scan is more precise — always follow the guidance of your midwife or doctor.
Common questions
How is my due date calculated?
From the first day of your last menstrual period (LMP), your due date is about 280 days (40 weeks) later — Naegele’s rule. If your cycle is longer or shorter than 28 days, we shift the estimate by the difference, since ovulation timing moves with cycle length.
How accurate is a due date calculator?
It’s an estimate. Only about 1 in 20 babies arrive on their exact due date; most arrive within roughly two weeks either side. An early ultrasound dating scan is more accurate, especially if your cycle is irregular.
Does Fawna store my dates?
No. This calculator runs entirely in your browser — your dates are never sent to a server or saved. That’s how Fawna treats reproductive data everywhere: private by default.
Fawna raises your daily targets as your pregnancy progresses — about +340 kcal in trimester 2 and +452 in trimester 3, plus more iron and folate. Join the early-access list.