Pregnancy Due Date Calculator

Enter your last menstrual period or conception date to find your estimated due date based on 280 days (40 weeks), with your current pregnancy week and trimester.

Select the date your last period started

Use 28 days (default) if unsure

How to Use

  1. Select date type

    Choose whether to calculate from your last menstrual period or estimated conception date.

  2. Enter the date

    Select the relevant date from the calendar.

  3. View results

    See your estimated due date, current pregnancy week, and trimester information.

What is an estimated due date?

The estimated due date (EDD) is the date your baby is expected to be born, set at 280 days (40 weeks) after the first day of your last menstrual period (LMP). Although pregnancy actually begins at ovulation and conception, the exact ovulation date is hard to pin down, so clinicians use the easy-to-remember LMP as the reference. As a result, the stated gestational age runs about two weeks ahead of the actual moment of conception.

Why the due date matters

  • Prenatal test scheduling: screening tests, detailed ultrasounds and gestational diabetes tests are all timed to specific weeks of pregnancy.
  • Fetal growth assessment: it serves as the benchmark for comparing whether the measured fetal size matches the expected gestational age.
  • Timing of delivery: it distinguishes preterm birth (before 37 weeks) from post-term pregnancy (42 weeks or more).

Keep in mind that the due date is not a fixed appointment but the center of a range. Only about 5% of babies arrive on the exact day, and most are born within two weeks before or after the estimated date.

Calculation formula

Naegele's rule is applied to the last menstrual period along with a menstrual-cycle correction.

Due date = last menstrual period + 280 days + (cycle length - 28)

Example: if the last menstrual period was 2026-01-01 and the cycle length is 32 days, the cycle correction is 32 - 28 = +4 days. So you add 280 + 4 = 284 days, giving a due date of 2026-10-12.

  • 280 days: average length of pregnancy (40 weeks)
  • cycle length - 28: corrects for the difference from a standard 28-day cycle (a longer cycle means later ovulation and conception, pushing the due date back)
  • estimated conception date = last menstrual period + 14 days + cycle correction

The current gestational age is shown as the quotient (weeks) and remainder (days) of (today - last menstrual period) / 7.

Frequently Asked Questions

How is the due date calculated?
Following Naegele's rule, 280 days (40 weeks) are added to the first day of your last menstrual period. If your cycle differs from 28 days, the date is corrected by that difference for a more accurate estimate.
How accurate is the estimated due date?
The due date is the 280th day from the LMP, and birth usually happens within two weeks before or after it. Only about 5% of babies are born on the exact due date, and an early ultrasound can refine the estimate.
What are pregnancy trimesters?
They divide the pregnancy into three parts: the first trimester (weeks 1-12) when the major organs form, the second trimester (weeks 13-27) when the baby grows rapidly, and the third trimester (weeks 28-40) when the body prepares for birth.
What if my menstrual cycle is irregular?
If your cycle is irregular, enter your usual average cycle length, or have an ultrasound measure the fetal size (CRL) to determine gestational age more accurately. This calculator includes a cycle correction, so entering your usual cycle gives an adjusted due date.
Which should I trust if the ultrasound differs from the calculation?
An early ultrasound (weeks 7-12) is generally the most accurate. If the LMP-based calculation and the ultrasound differ by 7 days or more, clinicians usually revise the due date based on the ultrasound.
What happens if I pass my due date?
Going one to two weeks past your due date is within the normal range. However, beyond 42 weeks (294 days) placental function can decline, so induction or a cesarean is usually considered between 41 and 42 weeks. Always consult your care provider once you pass your due date.
Why is a cycle-length correction needed?
Naegele's rule assumes a standard 28-day cycle with ovulation on day 14. If your cycle is longer, such as 32 days, ovulation and conception are delayed by that much, so the cycle difference (e.g. +4 days) is added to the 280 days to push the due date back closer to reality.
How is the estimated conception date determined?
In a standard 28-day cycle, ovulation occurs about 14 days after the start of the last period, so the estimated conception date is calculated as 'last menstrual period + 14 days + cycle correction'. Because sperm can survive for several days, the actual moment of conception may vary by a few days.
Updated 2026 — WHO standards

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