About the Conception Date Calculator
Estimated conception date and fertile window from the last period or a known due date.
Also known as: when did i conceive, conception calculator, date of conception.
How to use this calculator
- Enter i know the, date, cycle length.
- The result updates instantly as you type — press Calculate (or Enter) at any time.
- Review the breakdown shown under the main result.
- Use Copy result or Share to save the answer or send a link with your inputs.
Formula
Conception ≈ ovulation ≈ LMP + (cycle length − 14 days)
Worked example
Using the values pre-filled in the calculator above:
- I know the: Last menstrual period
- Date: 2026-07-14
- Cycle length = 28 days
the calculator returns:
- Estimated conception: Tuesday, July 28, 2026
- Fertile window: Thursday, July 23, 2026 – Wednesday, July 29, 2026
- Due date: Tuesday, April 20, 2027