Conception Date Calculator
Estimate the conception date and window from a due date, last period or birth date, adjusted for cycle length. Educational only.
Last reviewed by the Radiatus Cloud team
Conception usually occurs around ovulation, ~14 days before the next period (adjusted for cycle length). Estimates carry a window of several days. Educational only — not medical advice.
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Estimate a conception date
Working out roughly when conception occurred is a common question in pregnancy. This calculator estimates the conception date and window from a due date, last period, or ultrasound date.
Why conception is a window, not a day
Conception cannot be pinned to an exact day, because it happens around ovulation and depends on timing that is not precisely known, so it is estimated as a window rather than a single date. Working backward from a due date, or forward from the last period, using standard pregnancy timing, gives that window. It is useful for curiosity and for understanding pregnancy dating, but it is an estimate with inherent uncertainty. For anything medical, the dates a healthcare provider establishes are what matter.
A health estimate
This is an estimate from a standard formula for general information, not medical advice; individual health depends on far more than any single number, so consult a professional for anything that matters. It runs entirely in your browser, so nothing you enter is uploaded, keeping your figures on your own machine.
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Frequently Asked Questions
Why is conception a window rather than a date?
Because it happens around ovulation and depends on timing that is not precisely known, so it is estimated as a range rather than a single day.
How is it estimated?
By working backward from a due date, or forward from the last period or an ultrasound date, using standard pregnancy timing.
How accurate is it?
It is an estimate with inherent uncertainty, useful for curiosity and understanding dating, but not a precise determination.
Is this medical advice?
No. It is a general estimate. The dates a healthcare provider establishes are what matter for anything medical.
Is my data uploaded?
No. The calculation runs entirely in your browser.
Privacy & Security
Runs entirely in your browser. No data is sent to any server.
How to Use
Choose what you know (due date, LMP or birth date), pick the date and your cycle length to see the estimated conception window.
Disclaimer: This tool is provided "as is" without warranty of any kind. Results are for educational and utility purposes.
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