Estimate when you conceived. This free conception date calculator works from your last period or due date and shows the likely conception window around ovulation.
This gives an estimated conception date for general interest. Conception usually happens around ovulation, but the exact day can’t be known for certain — the result is a best estimate and a likely window, not proof of a specific date.
Estimate from
days
Conception is estimated at ovulation — about 14 days before the next period would have started, or roughly 266 days before the due date.
Estimated conception date
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Enter a date
Likely conception window
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Estimated due date
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Implantation (approx.)
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Estimates only and not medical advice. The exact conception date can’t be confirmed; an early ultrasound and your healthcare provider give the most accurate pregnancy dating.
Use this free conception date calculator to estimate when you conceived. Work it out from your last period or your due date, and see the likely conception window.
What this conception date calculator does
A conception date calculator estimates the day you likely conceived — usually around ovulation. It works from your last period (ovulation about 14 days after it starts) or from your due date (roughly 266 days after conception).
How conception date is estimated
From last period: conception ≈ last period + (cycle length − 14)
From due date: conception ≈ due date − 266 days
For a last period on 1 June with a 28-day cycle, conception is estimated around 15 June — the same date you’d get working back from a 8 March due date.
Why it’s an estimate
Sperm can survive several days, so conception may not happen on the exact day of intercourse. The calculator gives a best-estimate date and a short window around ovulation, rather than a single guaranteed day.
Conception and implantation
Event
Timing
Ovulation / conception
~14 days before the next period
Implantation
~6–11 days after conception
Positive test
Around the time of a missed period
How to use the conception date calculator
Choose last period or due date.
Enter the date (and cycle length for the last-period method).
Read your estimated conception date and window.
Conception Date FAQ
How do I calculate my conception date?
Conception usually happens around ovulation — about 14 days after your last period starts, or roughly 266 days before your due date. The calculator works it out either way.
Can I find conception date from my due date?
Yes. Switch to "due date" mode and the calculator subtracts about 266 days to estimate when you conceived.
How accurate is a conception date?
It's an estimate. Because sperm can survive several days, conception may not be the exact day of intercourse, so the tool also shows a likely window.
Is the conception date the same as the day I had sex?
Not necessarily — conception happens when the egg is fertilised, which can be a few days after intercourse, around ovulation.
When does implantation happen?
Usually about 6–11 days after conception, when the fertilised egg attaches to the uterus. The calculator shows an approximate implantation window.
Is the conception date calculator free?
Yes, this conception date calculator is completely free, needs no sign-up, and gives instant results in your browser.
