Using the Pregnancy Conception Calculator
Enter the first day of bleeding for the last period and the usual cycle length. The model places ovulation about fourteen days before the estimated next period and adjusts the due-date estimate for cycle length. It assumes a regular pattern rather than measuring ovulation.
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
Why does the estimated conception window cover several days?
The calculator displays a window around its estimated ovulation date rather than one confirmed date. Actual cycle timing can vary, and the form has no biological measurements or clinical dating information. The window is illustrative, not proof of when conception happened.
Guide updated .