Conception calculator
Conception date calculator
Enter the first day of your last period or your due date to estimate when you conceived.
Updated
In short
How do I work out when I conceived?
Conception usually happens around ovulation, about two weeks after the first day of your last period in a 28-day cycle. From a due date, count back 266 days, or 38 weeks. Sperm can live up to five days, so the sex that led to pregnancy may have been up to five days before conception. The date is an estimate.
Your estimate
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This is an estimate, not a diagnosis or birth control.
General information, not medical advice. Your doctor or midwife can tell you what your own results mean.
How it's calculated
- From your last period: conception ≈ first day of last period + cycle length − 14 days.
- From your due date: conception ≈ due date − 266 days (38 weeks).
- Sex window = 5 days before conception through 1 day after, because sperm can live up to 5 days.
- A due date from an early ultrasound is more accurate than one from a period date.
Gyne learns your real cycle and adjusts these estimates as you log.
Frequently asked questions
Can I know the exact day I conceived?
Usually not. Unless you had fertility treatment, conception can only be estimated to within a few days, because sperm can live for up to five days and ovulation timing varies.
Is conception the same as the day I had sex?
Not always. Conception can happen up to about five days after sex, when the egg is released and meets sperm that are still alive.
Why is pregnancy counted from my last period and not from conception?
Because the date of a period is easier to know. Counting from the last period is the standard, so you're about two weeks pregnant at conception.
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