Health
Pregnancy Due Date Calculator
Enter the first day of your last menstrual period (or your conception date) to estimate your due date using Naegele's rule, see how far along you are, and get your trimester dates.
Quick answer: Your estimated due date is 280 days (40 weeks) after the first day of your last menstrual period, adjusted for your cycle length — or 266 days after conception. Only about 4–5% of babies arrive exactly on it.
- You are currently—
- First trimester ends—
- Second trimester ends—
Estimated with Naegele's rule (280 days from the last menstrual period, adjusted for cycle length). Only about 4–5% of babies arrive exactly on their due date — confirm timing with an ultrasound dating scan.
How it works
1. Date from your last period
Pregnancy is dated from the first day of your last menstrual period (LMP), not conception. Naegele's rule adds 280 days — 40 weeks — to the LMP, with an adjustment if your cycle is longer or shorter than 28 days.
2. Or date from conception
If you know the conception date (or IVF transfer date), the due date is 266 days later — the same 40 weeks minus the average two weeks between period and ovulation.
3. Track weeks and trimesters
The calculator shows how many weeks and days along you are today, when the first trimester ends (week 13) and the second (week 27) — the milestones most screening tests are scheduled around.
Frequently asked questions
How accurate is a due date?
It's a best estimate, not an appointment: only about 4–5% of babies arrive on their due date, and most come within two weeks either side. A first-trimester ultrasound is the most accurate dating method and may shift the estimate.
How many weeks pregnant am I?
Count from the first day of your last menstrual period — not from conception. If your LMP was 10 weeks ago, you're 10 weeks pregnant, even though conception happened about 8 weeks ago.
What if my cycles aren't 28 days?
Naegele's rule assumes ovulation on day 14 of a 28-day cycle. With a 35-day cycle you likely ovulated a week later, pushing the due date about a week out — this calculator applies that adjustment automatically.