The Conception Date Calculator estimates when you most likely conceived. Choose whether you know your due date or the first day of your last period, enter that date, and it works out your estimated conception date along with a likely conception window of a few days.
Because conception happens around ovulation, the exact day can’t be pinpointed, but this gives a close estimate. Everything runs in your browser, so none of the dates you enter are uploaded or stored.
How to estimate your conception date
- Choose whether to calculate from your due date or your last period.
- Enter that date.
- If using your last period, set your average cycle length.
- Read your estimated conception date and the likely conception window.
How the conception date is estimated
Conception happens at ovulation. Counting from your last period, that is about your cycle length minus 14 days. Counting back from your due date, conception is about 266 days earlier — that is 280 days of pregnancy minus the roughly two weeks before conception.
Since sperm can survive for several days and ovulation timing varies, the tool also shows a short window around the estimated date rather than a single certain day.
Why people estimate conception
- Curiosity about when a pregnancy began.
- Working back from a known due date given at an ultrasound.
- Understanding the relationship between last period, ovulation, and due date.
- Remember this is an estimate — only your doctor can date a pregnancy precisely.
Frequently Asked Questions
How is the conception date calculated?
From your last period, conception is estimated at about your cycle length minus 14 days later. From your due date, it is about 266 days earlier. Both point to the likely time of ovulation.
Can I know the exact day I conceived?
Not precisely. Because sperm can survive for days and ovulation timing varies, conception can only be narrowed to a window of a few days, which this calculator shows.
Does the conception date equal the ovulation date?
Effectively yes — conception occurs when the egg is fertilised shortly after ovulation, so the estimated conception date is centred on your ovulation day.
Is this medical advice?
No. This tool is for general information only. For accurate pregnancy dating, consult your doctor, who can use an ultrasound.