Conception Calculator
Estimate conception date from due date. Likely conception window based on pregnancy duration.
How to Use
Enter your values in the fields above and click Calculate to get instant results. All computations run locally in your browser. No data is ever uploaded or stored.
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Estimating Conception Date
The conception date can be estimated by subtracting 266 days (38 weeks) from your due date, or 14 days from the start of your last menstrual period. CalcSolver's conception calculator reverse-calculates from either a known due date or birth date to find the likely conception window.
Conception typically occurs 11-21 days after the first day of your period, during the fertile window. The most likely day is day 14 for a standard 28-day cycle, but this varies significantly with cycle length. A 35-day cycle ovulates around day 21, not day 14.
Knowing your conception date helps establish accurate pregnancy dating, which affects timing of prenatal tests, ultrasound scheduling, and delivery planning. If you know your due date, use this calculator to find the conception window. See CalcSolver's pregnancy calculator for your full pregnancy timeline.
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Frequently Asked Questions
How is the conception date estimated?
The conception date is estimated by counting back from the due date or forward from the last menstrual period (LMP). Ovulation typically occurs about 14 days after the start of the LMP, so conception usually happens around day 14 of a 28-day cycle.
How accurate is a conception calculator?
Conception date estimates have a margin of error of several days because sperm can survive up to 5 days in the reproductive tract, and the exact ovulation date varies between cycles.
Can I determine the exact conception date?
The exact date cannot be determined with certainty unless conception occurred through assisted reproduction with a known transfer date. Ultrasound measurements provide the most accurate dating.