Conception date calculator
You most likely conceived about 266 days (38 weeks) before your due date, which is usually around 2 weeks after the first day of your last period. The sex that led to pregnancy most likely happened in the 5 days before that, or on the day itself.
How conception dates are worked out
Conception happens when sperm meets the egg, within about a day of ovulation. Sperm can survive inside the body for up to 5 days, so sex up to 5 days before ovulation can lead to pregnancy. That's why a conception calculator gives a window of days rather than a single date.
The most reliable way to date a pregnancy is a dating scan in the first trimester. If your due date was set by a scan, enter that due date above for the most accurate estimate.
Why the date is only an estimate
- Ovulation can happen earlier or later than usual in any cycle.
- Cycle lengths vary, especially after stopping contraception or while breastfeeding.
- Scans can be a few days out either way.
If you need to know the date for an important reason, talk to your doctor, who can look at your scan results.
Conception questions
How do I work out when I conceived?
Count back 266 days (38 weeks) from your due date, or count forward about 14 days from the first day of your last period if your cycle is 28 days. Conception happens within a day of ovulation.
Can a conception calculator tell me the exact day?
No. Even with a known due date, conception can only be estimated to within a few days, because ovulation varies and sperm can live for up to 5 days. If you had sex on several days around that time, any of them could be the day.
Can a scan show when I conceived?
A dating scan in the first trimester measures your baby and is accurate to within about 5 days. It gives a more reliable estimate than your period date, especially if your cycles are irregular.
Can I get pregnant from sex after ovulation?
Only for about 12 to 24 hours after ovulation, while the egg survives. Most pregnancies come from sex in the days before ovulation.
Why is my conception date 2 weeks after my last period?
Because ovulation usually happens about 2 weeks after your period starts. Pregnancy weeks are counted from your period, so you conceive at about 2 weeks pregnant.