Conception calculator.
Use this free conception calculator to get fast estimates, compare scenarios, and understand the numbers with clear step-by-step context.
Use the Conception Calculator.
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About the Conception Calculator
A conception calculator estimates when conception likely occurred, working either forward from the first day of your last menstrual period or backward from a known due date. It is useful for understanding pregnancy timing, though conception can only ever be estimated within a window of a few days.
How it works
From a last menstrual period (LMP), conception is estimated at roughly day 14 of the cycle (adjusted for your cycle length), with a due date about 280 days after the LMP. From a due date, conception is estimated about 266 days earlier. Ovulation timing naturally varies, so treat the date as approximate.
Reading the chart
Alongside the estimated conception date you get the matching due date, LMP, and a conception window covering the most likely days.
⚠ Disclaimer: This calculator provides general estimates for education only and is not medical advice. Individual needs vary with health conditions, medication, and body composition. Consult a qualified healthcare professional before making health, nutrition, or medical decisions.
FAQ
How exact is the conception date?
It is an estimate within roughly a five-day window, since sperm can survive several days and ovulation timing varies between cycles.
Does cycle length matter?
Yes. Longer or shorter cycles shift ovulation and therefore the conception estimate, which is why the calculator asks for your average cycle length.
Is this a reliable paternity tool?
No. For any medical or legal certainty about timing, use ultrasound dating and professional testing rather than a calendar estimate.