A familiar situation
Use cycle dates to estimate likely ovulation timing, not an exact fertilization date.
How to use this calculator
- Enter first day of last period, usual cycle length.
- Select Calculate to see the answer and its breakdown.
- Keep a scenario, change an input and compare the results.
Use consistent units and check the assumptions below before applying the result.
How conception is calculated
The estimate places ovulation about 14 days before the next expected period; conception is most likely around ovulation, with a wider possible window because sperm can remain viable for several days. A 30-day cycle usually places the estimated ovulation around cycle day 16, rather than day 14.
Estimated ovulation≈LMP+cycle length−14 days.A 30-day cycle usually places the estimated ovulation around cycle day 16, rather than day 14.
Assumptions & useful context
This estimates likely timing from a cycle; it cannot determine exact conception.
Health calculations are estimates for education. They cannot diagnose a condition or replace a clinician’s assessment. Individual needs vary, especially during pregnancy, illness and growth.
Frequently asked questions
Can this determine paternity?
No. It is not precise enough for that purpose.
Why provide a window?
Ovulation and fertilization are not known from a calendar estimate alone.