Conception Date Calculator
Estimate your likely conception window from a due date, or forward from your last period.
About this calculator
This calculator estimates a conception window, not a single exact day, since conception typically occurs within a few days around ovulation. From a due date, it works backward using the standard 280-day pregnancy length; from a last menstrual period, it assumes a typical 28-day cycle with ovulation around day 14. Actual cycle length and ovulation timing vary by person.
The fertile window is about six days long: the five days before ovulation and the day of ovulation itself. Sperm can survive in the reproductive tract for up to about five days, while an egg can only be fertilized for roughly 12 to 24 hours after it's released. That's why conception is estimated as a range rather than a specific day, and why intercourse several days before ovulation can still lead to pregnancy.
Ovulation tends to happen about 14 days before the next period starts, rather than a fixed number of days after the last one. In a 32-day cycle, that means ovulation around day 18, not day 14. If you track ovulation with tests or basal body temperature, you'll have a more accurate picture than this calculator's standard-cycle assumption. For medical purposes, pregnancy is still dated from the last menstrual period, or from an early ultrasound.
Frequently asked questions
- Why is this a window instead of one exact date?
- Conception can only happen within a few days around ovulation, and sperm can survive in the body for several days beforehand, so a ±3 day window is a more realistic estimate than pretending to know an exact day.
- Does this account for irregular cycles?
- No, it assumes a standard 28-day cycle with ovulation on day 14. If your cycle is significantly longer or shorter, your actual conception window will shift accordingly.
- Can this tell me who the father is?
- No. A conception window based on dates can't reliably determine paternity, especially when possible dates are close together, because cycle length, ovulation timing, and sperm survival all vary. Only a paternity test can establish that.