Skip to content
PreggieLover

Free calculator

Conception date calculator

Estimate when you most likely conceived, from your due date or the first day of your last period, along with the window of days it probably happened.

Calculate from

Private: the calculation runs in your browser. Nothing you enter is sent or saved.

How we estimate your conception date

  • From your due date: conception = due date - 266 days (38 weeks), because pregnancy lasts about 38 weeks from conception.
  • From your last period: conception = first day of your last period + your cycle length - 14 days, which is when ovulation usually happens.
  • Likely window: from 5 days before to 1 day after the estimated date, since sperm can survive for up to about five days and an egg for about a day.

Next, see how far along you are or work out your due date from another date.

Frequently asked questions

Can this tell me the exact day I conceived?

No calculator can. Conception happens around ovulation, and sperm can live for several days, so the intercourse that led to your pregnancy may have been up to about five days before conception. That is why we show a window as well as an estimated date.

Is conception the same day as intercourse?

Not always. Fertilisation happens when sperm meets the egg after ovulation, which can be a few days after sex.

Which is more accurate: due date or last period?

If your due date comes from an early ultrasound scan, start from that. Otherwise the first day of your last period, adjusted for your cycle length, gives a good estimate.

Related reading

The PreggieLover app

Carry this season with you

Get week-by-week guidance, a daily scripture, prayer and declaration, and gentle care tools in the PreggieLover app.

Coming soon

We are putting the finishing touches on the app and waiting for the store to welcome it. It will be here very soon - thank you for your patience.

Use PreggieLover in your browser Try our free calculators