Pregnancy

Due Date Calculator.

Estimate your pregnancy due date based on your last menstrual period or conception date.

First Day of Last Menstrual Period (DD-MM-YYYY)

Average Cycle Length (days)

Quick Presets

Overview

About Due Date Calculation.

A pregnancy due date is estimated at 40 weeks (280 days) from the first day of your last menstrual period (LMP). Conception typically occurs about 2 weeks after LMP. Only about 5% of babies arrive exactly on their due date — it's an estimate, not a guarantee. This calculator uses the standard Naegele's rule: LMP + 280 days = estimated due date.

Methodology

How the Pregnancy Due Date Calculation Works

This calculator estimates your expected delivery date using Naegele's rule, which calculates 280 days (40 weeks) from the first day of your last menstrual period (LMP) and adjusts for your average menstrual cycle length. If you know your conception date, it calculates 266 days (38 weeks) from conception.

Frequently Asked Questions

Q1 How does the due date calculator calculate delivery dates?

By default, the calculator applies Naegele's rule: it adds 280 days (40 weeks) to the first day of your last menstrual period (LMP) and adjusts if your cycle is shorter or longer than the standard 28 days. When using conception date, it adds 266 days (38 weeks).

Q2 How accurate is an estimated due date?

An estimated due date is an approximation. Only about 4% to 5% of babies arrive on their exact estimated due date, while roughly 90% arrive within two weeks before or after. Clinical ultrasound measurements in the first trimester may refine your official clinical due date.

Q3 What is gestational age versus fetal age?

Gestational age is measured from the first day of your last menstrual period (LMP), meaning you are considered roughly 2 weeks pregnant at the moment of conception. Fetal age (or embryonic age) begins at actual fertilization and is approximately two weeks shorter than gestational age.

Q4 How does menstrual cycle length affect the estimated due date?

The standard formula assumes a 28-day cycle with ovulation on day 14. If your cycle is 32 days, ovulation typically occurs around day 18, shifting your due date approximately 4 days later. If your cycle is 24 days, ovulation is earlier, shifting the due date 4 days sooner.

Q5 What are pregnancy trimesters and how are they split?

Pregnancy is divided into three trimesters: the first trimester spans weeks 1 through 12, the second trimester covers weeks 13 through 27, and the third trimester encompasses weeks 28 through birth (typically week 40).

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