PureCalc
Women's Health

Pregnancy Due Date Calculator

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Written byPureCalc Editorial Team

Updated: September 9, 2026 • Educational calculator

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

Choose the date you know

Use LMP for the first day of the last menstrual period, conception for a known conception date, or IVF for the transfer date and embryo age. A transfer date is not the fertilization date. Your care team may revise the estimate using ultrasound findings.

days

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: Adding 280 calendar days to January 1st, 2024 gives October 7th, 2024.

Sarah's estimated due date is October 7th, 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.