Pregnancy Calculator
Enter a valid date.
This uses Naegele's rule (last period + 280 days), the standard estimate assuming a typical 28-day cycle — an ultrasound-confirmed due date from your provider is more accurate if you have one. Only about 5% of babies arrive exactly on the estimated due date.
Free pregnancy calculator that works both directions — from your last period to a due date, or backward from a known due date to your estimated conception window — with current gestational age and trimester shown either way.
How it works
- Choose whether you know your last period date or an existing due date
- Enter that date
- See your due date, current gestational age, trimester, and estimated conception date
Frequently asked questions
What is Naegele's rule?
It's the standard method for estimating a due date: 280 days (40 weeks) after the first day of your last menstrual period, assuming a typical 28-day cycle. It's a widely used estimate, not a guarantee — only about 5% of babies are born exactly on their estimated due date.
Why does this calculator accept a due date as input?
If you already have a due date from an ultrasound or your provider, this lets you work backward to see your estimated conception date and track gestational age from that more accurate starting point instead.
Related tools
From the blog
Update history
- 2026-09-01 Added: a cover image — used as the card thumbnail, social share image, and blog title image.
- 2026-09-01 Launched: pregnancy calculator with dual input modes (last period or known due date), covering due date and conception date estimation in one tool. Entirely client-side.