Conception Date Calculator
Estimate the date your baby was conceived based on your due date or LMP.
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Result
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Formula
Back-calculates the approximate date of fertilization.
Worked Example
Estimating Conception Date
- Method 1 (Due Date): Subtract 266 days from the due date.
- Method 2 (LMP): Conception typically happens 14 days after the first day of your last period (for a 28-day cycle).
- Conception takes place when a sperm fertilizes an egg, usually within 24 hours of ovulation.
- The date of conception may not be the same as the date of intercourse, as sperm can live inside the body for several days.
These dates are scientific estimates; actual conception can vary by a few days depending on individual ovulation timing.
You can also calculate changes using our Pregnancy Due Date Calculator, Ovulation Calculator or Gestational Age Calculator.
Frequently Asked Questions
When did I conceive?
Most people conceive about 14 days after the start of their last period, or 38 weeks before their estimated due date.
Is intercourse date conception date?
Not necessarily. Since sperm can survive inside the body for up to 5 days, you may have had intercourse on Monday but not actually conceived until Wednesday.
How accurate is this?
If your due date was confirmed by an early ultrasound, the conception date estimate is highly accurate (within 3-5 days).
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I can help you understand the conception date calculator formula, interpret your results, and answer follow-up questions.
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