For it to work, obviously the budget has to be per month (for instance, $100/month), instead of an absolute limit. Most of the time, that's what you'd want: if

For it to work, obviously the budget has to be per month (for instance, $100/month), instead of an absolute limit. Most of the time, that's what you'd want: if you calculated that what you use will cost $50 each month, setting a budget of $100 per month would give some room for growth while preventing billing disasters (and you can always increase it a bit if necessary).