EachCalculatorPregnancy Conception Calculator
Estimate the likely conception date from either your due date or the first day of your last menstrual period.
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Enter a date to estimate conception.
How It Works
From a due date
Conception is estimated as 266 days (38 weeks) before the due date, since a full-term pregnancy is typically counted as 40 weeks from the last period but only about 38 weeks from conception.
From your last period
Conception is estimated as 14 days after the first day of your last period, based on typical ovulation timing in a standard 28-day cycle.
Example Calculation
For a due date of October 8, the estimated conception date is around January 15 of that same year.
Common Mistakes
- Treating the estimate as an exact date — ovulation timing varies between individuals and cycles, so this is a reasonable estimate, not a certainty.
- Using an irregular cycle length without adjustment, which shifts the actual ovulation window earlier or later than the standard 14-day assumption.
Frequently Asked Questions
- How accurate is this estimate?
- It's based on typical ovulation timing for a standard cycle, so it gives a reasonable estimate window, but actual conception can occur several days earlier or later depending on individual cycle variation.
- How is this different from the Pregnancy Due Date Calculator?
- The Due Date Calculator works forward from your last period to estimate your due date. This calculator works backward — from a due date or last period — to estimate when conception likely occurred.