How is conception date estimated?

Medical dating assumes conception about 14 days after LMP for cycle-based estimates, or 266 days before the due date when working backward from EDD.

Can conception date be exact?

Sperm can survive up to 5 days and ovulation timing varies, so conception is a window of several days, not a single calendar day.

No. Use our IVF due date calculator for embryo transfer-based dating.

Find your estimated conception date from due date or last menstrual period.

Calculate From

Date

Conception Date

Wednesday, Aug 19, 2026

Due Date

Wednesday, May 12, 2027

How to use this calculator

Frequently Asked Questions

How to Use

What it calculates

Estimates when conception occurred from either your last menstrual period or a known due date.

When to use it

Use when curious about conception timing, planning a pregnancy announcement, or filling in medical history forms.

Formula

Conception ≈ LMP + 14 days, or due date − 266 days (Naegele-based estimate).

Example

Due date December 15 → estimated conception around March 24 (266 days earlier).

Explore More

Calculate pregnancy weeks and days from your last menstrual period.

Estimate your implantation window from ovulation or last menstrual period.

Calculate your estimated due date from embryo transfer day (3-day or 5-day).

Calculate your next period date and cycle info from your last menstrual period.

Calculate your last menstrual period from a known due date.

Estimate fertile and safe days using the calendar method (educational only).