Due Date Calculator
Your due date is the estimated day you reach 40 weeks. Enter the first day of your last period and the calculator applies Naegele’s rule — plus shows how far along you are today.
Your numbers
Result
- Gestational age now
- Enter the first day of your last period.
- Trimester
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- Estimated conception
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How the due date is calculated
The standard method is Naegele's rule: add 280 days (40 weeks) to the first day of your last menstrual period (LMP). Equivalently, subtract 3 months and add 7 days. Pregnancy is dated from the LMP, not from conception, which is why "40 weeks pregnant" is really about 38 weeks since the egg was fertilized.
Only an estimate
The due date is a best estimate, not a deadline. Only about 1 in 20 babies arrive on it; most come in the two weeks either side. An early dating ultrasound (weeks 8–13) is more accurate than the LMP, especially if your cycle is irregular — your provider will use it to confirm or adjust the date.
Gestational age and trimesters
Gestational age counts weeks and days from the LMP. The trimesters split roughly as: first up to 13 weeks, second 14–27 weeks, third 28 weeks to birth. Change the reference date to see how far along you were, or will be, on any day.
Informational and educational result. Not a substitute for professional advice.
Frequently asked questions
Sources
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Copy the code and paste it into your site or blog. Credit with a link back to Contania is included, and the height adjusts itself.
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Gestational Age
Find out how many weeks and days pregnant you are from the first day of your last period, with the trimester and the estimated due date.
CalculateConception Date
Estimate when conception likely happened, from your last period or your due date. See the most likely date and the window around it.
CalculateOvulation
Find your ovulation day and fertile window for the next three cycles from your last period and cycle length. A planning estimate for trying to conceive.
CalculateFertility Window
Find your fertile window and peak fertility days from the first day of your last period and your cycle length — the best days to try to conceive.
Calculate