Health & Fitness

Conception Date Calculator

Estimate your conception date.

Enter your due date or the first day of your last menstrual period to estimate your likely conception date.

Select a valid date.

Estimated Conception Date

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Approximate — actual conception can vary by several days

How to Use This Tool

  1. Choose whether you know your last menstrual period or your due date.
  2. Enter the corresponding date.
  3. Click Calculate for your estimated conception date.

How Conception Date Is Estimated

From Last Menstrual Period: Conception ≈ LMP + 14 days (approximating typical ovulation timing)

From Due Date: Conception ≈ Due Date − 266 days (the standard 280-day/40-week pregnancy length minus the ~14 days from LMP to ovulation/conception)

Why This Is Approximate

Actual ovulation and conception timing varies between individuals and cycles, and due dates themselves are estimates (only a small percentage of babies are born exactly on their due date) — this calculator provides a reasonable approximation, not an exact determination.

Uses for This Estimate

This calculation is sometimes used for general reference, timeline planning, or curiosity — for legal or medical purposes requiring precise conception dating, consult a healthcare provider, as more precise methods (like early ultrasound dating) are far more reliable.

Frequently Asked Questions

How accurate is this conception date estimate?

It's a reasonable approximation based on typical ovulation timing, but actual conception can vary by several days from this estimate — for precise dating, an early pregnancy ultrasound is significantly more accurate.

Why use 266 days instead of 280 days from the due date?

The standard 280-day (40-week) pregnancy length is counted from the last menstrual period, not from conception — since conception typically occurs about 14 days after the LMP, working backward from the due date requires subtracting 266 days to reach conception, not the full 280.

This calculator is provided for general informational and estimation purposes only. Results should not be treated as professional financial, tax, legal, medical, or engineering advice. Always verify critical calculations with a qualified professional or official source before making decisions.