Alot of people worry about the exact percentage..ast stated there is a generally agreed upon acceptable range of FOC of around 8-13% with 10% being about optimum.

But here's something you can go by that is much easier than figuring out all the formulae and whatnot.

Make sure you have at least 2.5 times as much weight on the point end of the arrow as you do on the back..include your point and insert weight, and compare it to the weight of your nock, unibushing if you use one, and your fletches.

You can get up to around 5 times as much point vs. nock end..but below 2.25 or so and you will likely run into FOC issues. The shorter the arrows, the less you can get away with, the longer your arrows, the more you'll want to get up to 3 to 5 times as much weight point vs. back.