What does it take to drop out of Division V?

I just reached platinum. By a lot of hard work I managed to do it. Played kayle a lot, but sometimes forced to grab support since I'm not equally as good plat in any other lane. With the upcomming nerf on Kayle I fear I won't stay for long. How many losses does it take to drop out of this league? I'm currently on a losstreak and taking a break. 7 losses the last days. In a row.