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Conception date calculator

When did I conceive?

Work back from your due date, your last period, a scan or an IVF transfer. You'll get the day conception most likely happened, and the days around it that could have led to it.

The date your clinician gave you, ideally from a scan.

Pick how you'd like to date it to see when conception most likely happened.

How it's worked out

A pregnancy is dated from the first day of the last period, and conception usually comes about two weeks after that, when you ovulate. Put the other way, conception is about 38 weeks, or 266 days, before the due date.

That gives the most likely day. Because sperm can survive up to five days and the egg about one, sex on any of the five days before that day, or the day after, could have led to the pregnancy. That's the window the calculator shows.

Which date to start from

If you've had a scan in the first trimester, start from the due date it gave you: it measures how far along the pregnancy actually is. If you're working from your last period, the answer depends on when you ovulated that cycle, which may not have been day 14. IVF dates are exact. No due date yet? The due date calculator gives you one.

A note on certainty

This is an estimate, and people sometimes need more than that. If you're trying to work out paternity between two dates close together, the calendar can't settle it. A prenatal DNA test can, from a blood sample, and your clinician can tell you how to get one.

Questions people ask

How do I work out when I conceived?

Conception happens around ovulation, about 266 days (38 weeks) before your due date, or roughly two weeks after the first day of your last period in a 28-day cycle. Your due date, if you have one from a scan, gives the most reliable answer.

Can sex five days before ovulation get me pregnant?

Yes. Sperm can survive up to about five days, so conception can come from sex in the days before ovulation as well as on the day. That's why the calculator shows a window of days, not one.

Can a conception date tell me who the father is?

Not reliably when the possible dates are within a couple of weeks of each other. Ovulation moves from cycle to cycle and sperm can wait days, so the windows overlap. A DNA test, which can be done during pregnancy, is the only way to know.

My ultrasound date doesn't match when I thought I conceived. Which is right?

A first-trimester scan is usually the better guide. Ovulation can come earlier or later than the calendar suggests, which shifts conception by days either way.

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