Useful formulas I've added recently:
Personal troop upkeep:
=roundup((((F2^1.03) * 1.8) - 100) / 24)
(input the number of troops you have into "F2", in this case, and the formula tells you how much it costs per turn)
Fief troop upkeep:
=roundup((((F2^ 1.02) * 1) - 100)/24)
Number of troops per upkeep (input the upkeep you want to pay and it calculates max number of troops you should have)
Personal:
=rounddown((((J2 * 24) + 100) / 1.8)^(1/1.03))
Fief:
=rounddown(((J2 * 24) + 100)^(1/1.02))
Replace columns with whatever works for you, of course.
I recommend creating a separate tab for this stuff.
I *think* these are all correct. That is, the formulas are from chadz post but the rounding is sort of an assumption. 50 troops actually comes out to like .05 upkeep or something but I think chadz rounds it up, so 50 troops = 1 upkeep (but you can actually have up to 60 troops and still only pay 1 upkeep. At 61, it becomes 2 upkeep.)