Ovulation Calculator
First day of your last period
Usual cycle length
days
First day of one period to the first day of the next.
Luteal phase length
days
The second half of the cycle: ovulation day = cycle length minus this. Far steadier than the cycle as a whole, which is why it is the thing to count back from.
Today
Estimated ovulation
Tue, October 20, 2026
Show the work
Ovulation Calculator
by Rule Calculator