When is it safe to rely on an income that changes with the market

I am 26, married and make $34k-$39k yearly, depending on OT worked, my wife is 25 and makes $50k-$55k, depending on OT worked, and we live comfortably with this amount.I won't go into details about what the investment is, because last time I asked it was questioned on wether or not this was real, instead of answering the actual question.So my question is this, if I am to rely on an income that may raise or drop from week to week, and I would like to make at least as much money on a bad week as I am making at my current job now, I know without actual numbers that is a bit tough to answer, but is there a general rule of thumb, maybe something like "make enough to be able to pay all bills for the month plus 10% more if it's a low week/month", or maybe " have a weekly average of 3 times what you need to pay your bills" via /r/business http://ift.tt/2rcR0uE