It would depend on where in the country you live I would guess.
We live in NY and Oct is the last month I use Frontline Plus until
next April giving Buddy's body a break.
I have never seen a tick or flea on him during those months.
It's starting to get cold here now however we can always get
an Indian Summer, which I'm hoping for
So between Nov-April
we stop. Hopes that helps you.