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Conception Calculator

Estimate the likely date of conception from a due date or from the first day of your last period.

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Conception Tool

Reverse Dating from Due Date or LMP

About the Conception Calculator

Estimate the likely date of conception from a due date or from the first day of your last period.

How to use the Conception Calculator

  1. Choose the Method: Known Due Date or Last Period (LMP).
  2. Enter the Given Date.
  3. Press Estimate Date.

Formula and method

Conception usually happens about 14 days after the last period starts (in a 28-day cycle), which is about 266 days before the due date.

Tips

  • The result is an estimate. Ovulation timing varies from cycle to cycle.

Frequently asked questions

How accurate is the estimated date?
It gives a window of a few days. Only an early ultrasound can date a pregnancy more precisely.