Free tool · No sign-up
Due Date Calculator
Estimate your due date, gestational age and trimester — from your last period, a conception date, an IVF transfer, or a dating scan. Private and free — nothing is saved unless you choose to.
How the due date calculator works
- How is my due date calculated?
- From your last period we use Naegele's rule — 40 weeks (280 days) from the first day of your last period, adjusted for your cycle length. From a conception date we count 266 days. From an IVF transfer we count 263 days (day-3 embryo) or 261 days (day-5 blastocyst). From a dating scan we add however many days remain to reach 40 weeks.
- How accurate is a due date estimate?
- It's an estimate: only about 1 in 20 babies arrive exactly on their due date, though most arrive within a week or two either side. A dating scan gives the most accurate estimate and may revise your date.
- Can I use an IVF transfer or scan date?
- Yes. Choose “IVF transfer” and pick day-3 or day-5, or choose “Ultrasound date” and enter the scan date plus the gestational age it measured (weeks and days).