PureCalc
Women's Health

Pregnancy Due Date Calculator

PC

Written byPureCalc Editorial Team

Updated: April 27, 2026 • Verified Clinical Formula

Calculate your estimated due date (EDD) based on your last menstrual period, conception date, or IVF transfer date using standard clinical formulas.

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Estimated Due Date

Select a date to calculate your EDD

How is Your Due Date Calculated?

Your Estimated Due Date (EDD) is a clinical approximation. In reality, only about 4% to 5% of babies are born on their exact due date. A typical full-term pregnancy lasts approximately 280 days (40 weeks) from the first day of your last menstrual period (LMP).

Obstetricians and midwives use several standardized clinical formulas (such as Naegele's rule) depending on what data is available (LMP, known conception date, or IVF transfer dates).

Clinical Methods of Calculation

The method used to estimate your delivery date changes based on the specifics of how the pregnancy was conceived:

1. Last Menstrual Period (LMP) - Naegele's Rule
Formula: First day of LMP + 7 days - 3 months + 1 year (or simply +280 days). Assumes a standard 28-day cycle.
2. Exact Conception Date
Formula: Conception Date + 266 days (38 weeks).
3. IVF Transfer
Formula: Transfer Date + 263 days (for a Day-3 embryo) OR + 261 days (for a Day-5 embryo).

A Practical Example

Consider Sarah, who is trying to find her estimated due date using the standard LMP method. The first day of her last period was January 1st, 2024.

Using Naegele's rule: January 1st + 7 days = January 8th. Subtract 3 months = October 8th.

Sarah's estimated due date is October 8th, 2024. Note that if she goes to her 8-week dating ultrasound and the fetal crown-rump length indicates a different gestational age, her OB-GYN may officially revise this date.