Upkeep from Normal [Gold Cost] units which is 1/15th of the initial cost of the unit (60 Gold = 4 Upkeep)
The second is Sacred Units (Those with the Sacred or "Priest Levels" symbol in their special abilties) their upkeep is 1/30th of the Initial gold cost of the unit (60 Gold = 2 Upkeep).
Summoned monsters may or may not have upkeep depending on if they have been given an initial gold cost (even though you don't pay it, you summon the monster). My guide has most of the summoned upkeeps to a degree of +-.20 accurate (that means I summoned 5 of them and if I didn't see a change in upkeep I assumed it was 0).
Postscript to what Zen said: upkeep is not rounded down/up. So if a unit costs 35g, the upkeep is 1.166 (to however many decimal places the programmers track).
Originally posted by Kel: Sorry that it was asked already, I try to read up...searched on the wrong word.
No problem at all. You, unlike many, actually made the effort to do a search first. So I gave you the "proper" word to use. Then Zen came along and played the knight in shiny armor ...