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CalcivoTools

Conception Calculator : Estimate Conception & Fertile Window

The Conception Calculator reverse-engineers the estimated date of conception, ovulation day, and most probable fertile window based on your expected due date or ultrasound date.

Interactive Calculator

100% Client-Side Engine
Estimated Date of Conception
Jun 30, 2026
Calculated from due date: Mar 23, 2027
Likely Fertile Window
Jun 25, 2026 – Jul 1, 2026
6-day conception period
Estimated LMP Date
Jun 16, 2026
Last menstrual period
Gestational Basis
266 Days (38 Weeks)
Post-ovulation timeline

Step-by-Step Examples

Conception from October 8 Due Date

Calculating conception window for an October 8, 2025 estimated due date.

Inputs: Due Date: 2025-10-08
Result: Estimated Conception Date: January 15, 2025 (Fertile Window: Jan 10 – Jan 16, 2025)

Calculates 266 days prior to full-term 40-week delivery.

How to Use This Tool

  1. Enter your Estimated Due Date (EDD).
  2. Specify your average menstrual cycle length (default 28 days).
  3. Click Calculate to see your estimated conception window and ovulation date.

Frequently Asked Questions

From the exact date of conception, full term fetal development lasts approximately 266 days (38 weeks), while from LMP it is 280 days (40 weeks).

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