Due date calculator
Estimate your pregnancy due date and see how many weeks along you are.
This uses Naegele's rule (last period plus 280 days), adjusted for your cycle length. It's an estimate — your provider's date is definitive.
Estimated due date
How a due date is estimated
Pregnancy is measured from the first day of your last menstrual period (LMP), not from conception, because the LMP is easier to pin down. The standard estimate — Naegele's rule — adds 280 days (40 weeks) to that date. If your cycle is longer or shorter than the typical 28 days, the estimate shifts accordingly, since ovulation happens later or earlier in the cycle.
The formula
Worked example
If your last period started on 1 March with a 28-day cycle, your estimated due date is about 6 December — 40 weeks later. A 32-day cycle would push it four days later.
Frequently asked questions
How accurate is a due date calculator?
It gives a solid estimate, but only about 1 in 20 babies arrive on the exact date. Most births happen within two weeks either side. An ultrasound dating scan is more precise.
Is pregnancy counted from conception or the last period?
From the first day of your last menstrual period. That's roughly two weeks before conception, which is why 40 weeks is counted even though pregnancy lasts about 38 weeks from conception.
What if my cycle isn't 28 days?
Enter your actual cycle length. A longer cycle means later ovulation, so the due date moves later; a shorter cycle moves it earlier.
When do the trimesters start and end?
The first trimester is weeks 1–13, the second is weeks 14–27, and the third is week 28 until birth.
Health disclaimer: This calculator is a general estimate, not a medical diagnosis or a substitute for professional advice. See our full disclaimer and talk to a doctor or qualified clinician before acting on the result.