Conception Date Calculator
Conception Date Calculator estimates when conception likely occurred — either from your estimated due date or from the first day of your last period — along with the likely conception window.
Last updated: July 2026
A conception date calculator estimates the day you likely conceived. From a due date it counts back 266 days; from your last period it adds about 14 days to find your ovulation and conception window.
How to use Conception Date Calculator
- Choose whether to calculate from your due date or your last period.
- Enter the date (and cycle length if using your last period).
- Read your estimated conception date and window.
Frequently asked questions
How is conception date estimated?
From a due date we subtract 266 days (38 weeks). From your last period we add roughly your cycle length minus 14 days to estimate ovulation.
Can it tell the exact day?
No — conception can occur across a fertile window of several days, so it's an estimate, not an exact date.
Is my data stored?
No — all calculations run locally in your browser.
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