Estimate an ovulation day and fertile window from the first day of a period and cycle length.
Change the inputs that matter to your decision. Optional assumptions stay collapsed until you need them.
Use the first day of the last period and your typical cycle length.
Set this only when checking a past or future phase; blank uses today.
Select the first day of the last period.
Practical notes about the inputs, assumptions, and result.
This model uses five days before estimated ovulation through one day after. Actual ovulation timing can vary from cycle to cycle.
No. Calendar estimates are not reliable contraception. Use a clinician-approved method for pregnancy prevention or planning.
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