upkeep costs

how are unit upkeep costs calculated?

and how can i minimise them?

Each unit over a certain amount costs 1gpt. The only way to minimise them is not to build units over that limit. Otherwise, make more money to offset the costs.

thanks

do workers and catapults/trebs have an upkeep cost??

Yes, all units have an upkeep cost. Except slaves; captured workers and NONE settlers, popped from barb huts.

Upkeep works different in different governments. Check civilopedia for details for the different government.

If you are in Republic for example, you'll have:
1 free unit for every town (pop size 1-6)
3 free units for every city (pop size 7-12)
4 for every metropolis (size above 12)

In republic you pay 2 gold for each unit that doesn't get free support from your towns/cities.

If you're in monarchy, you'll pay 1 gold for every unit that doesn't get free support, and you'll have:
2 free unit for every town
4 free units for every city
8 for every metropolis

[Edit:] I think upkeep also changed in the different versions of Civ. What I wrote is is for C3C.

I believe that you do pay upkeep for popped settlers, but you don't pay for foreign settlers that you build out of captured cities. You don't pay upkeep for captured artillery either.

You don't pay for any captured or enslaved unit - anything flagged as having another nationality is maintenance-free. So England can build up a pretty substantial, free fleet of Man-o-Wars (Men-o-War?) if the AI decides to come out and play, and anyone can get quite a good stock of free privateers, as well, if you want to go that route.