👶
FREE CALCULATOR

Pregnancy Due Date Calculator

Calculate your pregnancy due date from your last menstrual period (LMP). See your current week, trimester, and key pregnancy milestones.

Advertisement
👶Pregnancy Due Date Calculator
Enter your last period date above

How to Calculate Your Pregnancy Due Date

The standard method for calculating a due date is Naegele's Rule: add 280 days (40 weeks) to the first day of your last menstrual period (LMP). This assumes a 28-day cycle. For longer or shorter cycles, adjust by the difference from 28 days.

Pregnancy is divided into three trimesters: First trimester (weeks 1–13), Second trimester (weeks 14–26), and Third trimester (weeks 27–40). Full term is considered 39–40 weeks, though births between 37 and 42 weeks are normal. Your due date is an estimate — only about 5% of babies are born on their exact due date.

An early ultrasound (before 13 weeks) provides the most accurate due date by measuring the fetal crown-rump length (CRL). If your ultrasound date differs from your LMP calculation by more than 5–7 days, doctors typically use the ultrasound date.

Pregnancy Timeline Overview

Frequently Asked Questions

How is the due date calculated?+
The standard method is Naegele's Rule: add 280 days (40 weeks) to the first day of your last menstrual period. This works best with a 28-day cycle. Ultrasound measurement before 13 weeks is more accurate and will override the LMP calculation if they differ significantly.
How many weeks pregnant am I?+
Count the number of days from the first day of your last menstrual period to today, then divide by 7. For example, if your LMP was 10 weeks ago, you are in week 10. Our calculator shows this automatically — along with your current trimester and days until your due date.
What is considered full term?+
Full term pregnancy is 39–40 weeks. Early term is 37–38 weeks; late term is 41 weeks; post-term is 42+ weeks. Births before 37 weeks are considered premature (preterm). Babies born at 37+ weeks are generally healthy, but 39–40 weeks is optimal for lung and brain development.
Can my due date change?+
Yes. If your first-trimester ultrasound shows a size inconsistent with your LMP date (by more than 5–7 days), your provider may adjust your due date. Late ultrasounds are less accurate for dating. Most providers keep the due date stable after the anatomy scan at 18–20 weeks unless there is a clinical reason to change it.

All Calculators

%
Percentage Calculator
⚖️
BMI Calculator
🏠
Mortgage Calculator
Advertisement

How a Due Date Is Calculated

The standard estimate (Naegele's rule) adds 280 days — 40 weeks — to the first day of the last menstrual period (LMP). Conception-based dating adds 266 days instead, and early ultrasound measurement is considered the most accurate method, especially when cycles are irregular.

Worked example

With an LMP of 10 October 2025, the estimated due date is 17 July 2026. Trimesters break at the end of week 13 and week 27.

Frequently asked questions

How many babies arrive on their due date? Only about 4–5%; the vast majority are born within two weeks either side, and first pregnancies often run past the date.

What if my cycles aren't 28 days? Naegele's rule assumes 28-day cycles with day-14 ovulation; longer or shorter cycles shift the estimate, which is why ultrasound dating frequently revises it. Always confirm dates with your healthcare provider.