[8organicbits]

I've had concurrent retainers, but I'd avoid over-stacking them. Retainers are a liability, you could have multiple clients ask for hours simultaneously, and you'll suddenly be very busy. Weekly retainers are better than monthly because they smooth out the hours.

Personally, I divide my availability into contracts and the more concurrent contracts I have, the more I pad for overhead. So one 40 hr/wk contract vs three 10 hr/wk contracts.

It's possible to stack more, as often retainers aren't fully used, but I think it risks the relationship with clients, which is worth more than over scheduling yourself.