Pregnancy Conception Calculator
Estimate your conception date and likely window from your due date or last period.
How the conception date is estimated
- From a due date: conception is about 266 days (38 weeks) before it.
- From your last period: conception is about ovulation, which is your cycle length minus 14 days after the period started. With a 28-day cycle that is day 14.
Because sperm can survive for up to about five days, the likely window runs from five days before the estimated date to one day after it.
Worked example
A due date of October 17, 2027 points to conception around January 24, 2027, with a likely window from January 19 to January 25. A last period that began January 10, 2027 with a 28-day cycle gives the same estimate.
Frequently asked questions
How accurate is this estimate?
It is approximate. Ovulation can vary from cycle to cycle, so the real conception date can differ by several days. An early ultrasound gives a better estimate.
Can this tell me who the father is?
No. The dates are estimates and cannot be used to determine paternity.
Why is there a window instead of one date?
Sperm can survive for several days and an egg is available for a short time, so conception can result from intercourse in the days before ovulation.
Can I use this to plan or avoid pregnancy?
It is not a reliable method for either. Talk to a doctor about fertility or contraception.
This calculator is for general information only and is not medical advice.