Using the Conception Calculator
Start with the first day of the last period, not the day bleeding ended. Changing the cycle length moves the next-period estimate and the assumed ovulation date. The calculator also displays a due-date estimate, which does not confirm that pregnancy has occurred.
Worked example
Use the example inputs below to reproduce this result. These are the form's starting values, not recommended targets. Changing your inputs updates your result above; this worked example stays fixed for comparison. Results are rounded for display.
Example inputs
- First day of last period
- 2026-01-01
- Typical cycle length (days)
- 28
Example result
- Estimated next period
- 2026-01-29
- Estimated ovulation
- 2026-01-15
- Estimated fertile window
- 2026-01-10 to 2026-01-16
- Estimated due date
- 2026-10-08
Method and assumptions
Assumes ovulation about 14 days before the next period and a regular cycle. Dates can vary considerably; this is not a reliable contraception method or confirmation of conception.
Treat the dates as calendar estimates
This model starts from a recorded period date and a chosen cycle length. It does not observe the biological events shown in the results. A neat date on the calendar can look more certain than the assumptions justify, especially when cycles vary. The projections are not confirmation of pregnancy and are not a reliable contraceptive method.
Common question
Does the result confirm that I ovulated?
No. The tool assumes an ovulation date from the calendar inputs; it does not detect ovulation. A date appearing in the results is a projection under that assumption, and actual timing may differ.
Guide updated .