Can someone explain this to me?

There are quite a few influences that can change income from turn to turn. The main one being mini freighter locations.

Then there are boarder movements, population changes, fleet changes, maintenance changes... thats all i can think of for now.

Andrew,

It can have to do with trade issues or if your economy is experiencing a boost in tax income due to an in-game event (i.e. entrepreneurs expanding business and so forth).

Im there with ya...its frustrating. But mystik is right, there's a host of different external influences at any given time acting on your freighters. One he didnt mention was if a particular freighter passes through the influence of one of you economic starbases; itll go up. Or maybe that civ youre trading with has made some bad choices on their end and the value is being effected that way.
As well as all those other things he listed..you build a new ship; your military spending goes up to cover the maintenance of it and the same goes for any improvement you build on any planet.

The economy is indeed complicated. No one mentioned the penalty for having over 20k in your treasury. If you're spending some turns but not others, jumps like you describe could be intermittent instances of that penalty.

If you want to learn more about GC2 economics without scouring this forum, try the Galciv wiki. It's slowly getting better all the time. Check out the Economy page and this swell chart Voxel made.

Given those numbers (the turn by turn oscillation), it probably is the 20K penalty that GW mentioned. You suffer a 20% drop in revenue if you have 20K or more in you treasury when you hit the turn button...

Well, that sucks. I have about 24K now, so should I buy some ships? I can't continually buy new ships - eventually every starbase is maxed out! I still have a surplus (about 300bc).

Yes it does! few people would dissagree either.

I would be happy if the economic penalty was high enough to allow for the purchase of just one of the most powerful warships capable of being designed.

I balked hard when I first learned about this "feature," but I'm at least halfway a sympathizer now. Well, maybe a little less than halfway, but close for sure.

Reasons I'm OK with the >20K treasury penalty: 1) Any human-style culture probably has limits on how much wealth elites can stash away before the producing classes create disorder. 2) Using your economic power actively can help keep you safe from the AIs. 3) It's a game; rules are like terrain on a cross-country run--you just have to deal or decide the game's not for you.

@Andrew Easterly: I started looking for ways to spend after I learned about this >20K thing, and since then I've never seriously lacked for useful-seeming places to put "excess" BC. Even if you don't have an economy that supports buying fancy warships outright, you can pour endless cash into social spending, ship upgrades, and foreign policy. When my income's around 300 BC and I've toppped the treasury, I can usually get by with looking for something to buy only every 4 to 8 turns.

But this economic penalty dousn't take into acound your civilisations growth! So comparing the starting empire to the final empire.... how many more times larger is it? and yet the economic penalty is the same? Bha! stupid!!

Social stuff is a good place to dump cash...And if your problem is severe enough you can just start buying monster ships. I have made it to a ship maintainance cost of 700-800K in a game turn before...

I have been a long time advocate that the limit should scale with your income.

good idea, also researching trade and and or economic technologies should increase it too.

Hay, I was trying to be diplomatic. Being "OK" with something is not the same as *liking* it I'm on record sharing Purge's opionion that

You could always try reducing taxes if you have too much money.

Or go on a shopping spree.

put all your money into Research and buy anything you want. Thats a big wast of mony but it should make you loss money fast.

Don't sweat it, i wasn't meaning to attack your post, this economic penalty just ticks me off!