Trade Route Formula Explained

I found this formula for the demo but I didn't want to post about it because I thought the game was supposed to factor in the capital size and that it would just be a demo bug.

Anyhow, this is a bit of a shame. I thought the capital would have some influence on it. I wonder why they didn't use an actual 1.25 but something like 1.253 or so, might still be a bug?

Thanks for the info Dan and welcome to the boards!

Just wanted to add: the break-even point of a harbor buyout as soon as the city is built (420 gold) with an average of surplus food of X/turn (on standard speed) is given in the following table:

FpT - Turns Needed for profit after buying Harbor at pop 1 (unmodified):
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1.0 - 200 Turns
1.5 - 161 Turns
2.0 - 139 Turns
2.5 - 124 Turns
3.0 - 114 Turns
3.5 - 106 Turns
4.0 - 100 Turns
4.5 - 94 Turns
5.0 - 90 Turns
5.5 - 86 Turns
6.0 - 83 Turns

Looking at the above chart, you're probably thinking... Why are there diminishing returns on pumping more food quickly to cities? If anything, you'd think it opposite... follow the math:

Here's an extreme example to fetch the point:
New City is made and purchases a harbor for 420 Gold. You play golf with the mayor of every maritime C-S to the effect that it generates surplus +10 Food, on average.

By turn 4, it's already Size 3. It's just now starting to turn a profit (not much), because at size 2, the 3 gold upkeep on a harbor is still -.5/turn. We're still down 420Gold on our investment however

By turn 16 it turns size 6, but due to the 3.25GPT was earning our gross revenue is still only 23 gold.

On turn 30, we're up to size 8, revenue about 95 gold (but now we're up to 7 GPT)

Turn 40, Size 9... 158 Gold.

Turn 50, Size 10... 245 gold

Turns out we have to wait until turn 67 to our revenue to reach our initial 420G investment. Keep in mind, this is purely for trade purposes. In 67 turns, at that growth rate, the city will be massively profitable, just not from trade value before that time.

The moral of the story is that you for sure want to wait until Pop 3 to build the harbor, and may want to wait until pop 6-8 to buy one outright.

Note: Anybody feel free to check my math, no guarantees it's correct at such a late hour

And keep in mind that there are a couple of social policies that impact the relationship. There's one that reduces road maint and one that increases trade route income. Later in the game, trade income can support a lot of units to fuel the war machine.

@ necro: Route cost are discounted at anything lower than Prince difficulty (Chieftrain gets a 50% discount, for example). At what difficulty are you seeing the lower cost roads?

@ goodolarchie: interesting writeup, I'll probably add a link to your explanation in the first post after I have time to digest it.

@ rah: I'll try to get a list of modifiers in the first post at some point soon, but excellent point that there's a lot more to take into consideration as you advance

Updated first post with modifiers for difficulty, wonders, leader traits, and policies. Added section for harbors.

I would like to add that since you cant stack workers anymore, it may be better to work multiple connecting road tiles at once in order to get the connection up and running faster.

goodolarchie said:

Note: Anybody feel free to check my math, no guarantees it's correct at such a late hour

Click to expand...

I didn't check the math yet but if I you're planning to buy the harbor anyways, there's no point in waiting if you have the money - so your recommendation of waiting until the city grows is flawed. Yes, it will break even more quickly from the point of buying the harbor but unless you spend the gold on something more profitable in the mean-time you will lose the money the harbor would have yielded in those few turns. So if you're planning to buy, and don't have anything more profitable to spend on, by all means buy it the turn you build the city.

Of course, building the harbor with hammers is another question entirely.

Alpaca, even then, shouldn't one wait until the city is large enough to break even? By buying the harbor a few turns early, you introduce a new cost (maintenance) that exceeds the new revenue (trade route).

Thanks to the OP for a very helpful analysis!

I connect my cities mostly for the happiness bonus under Liberty. I think Commerce also decrease road upkeep.

One point on trade routes, sometimes the data doesn't seem to update until the turn after the trade route is made.

alpaca said:

I didn't check the math yet but if I you're planning to buy the harbor anyways, there's no point in waiting if you have the money - so your recommendation of waiting until the city grows is flawed. Yes, it will break even more quickly from the point of buying the harbor but unless you spend the gold on something more profitable in the mean-time you will lose the money the harbor would have yielded in those few turns. So if you're planning to buy, and don't have anything more profitable to spend on, by all means buy it the turn you build the city.

Of course, building the harbor with hammers is another question entirely.

Click to expand...

Well, it shouldn't take a TI-89 to see why buying out a harbor at anything less than 3 pop is going to lose you money! 2*1.25 doesn't outweigh the 3 upkeep. My point about the 6-8 recommended population for buying was that there will almost certainly be something better invested for your gold (i.e. market) that will earn you more profit at that point in time. That assumes you buy out buildings at all, which I really don't do. Still, the math is all there!

thank you very much, it's very helpful.

I have two questions about roads. Do i pay maintenance also for the roads outside my territory? How can i destroy the roads built by the ai after a conquest, if that roads are non usefull?

manarod said:

I have two questions about roads. Do i pay maintenance also for the roads outside my territory? How can i destroy the roads built by the ai after a conquest, if that roads are non usefull?

Click to expand...

You pay for them only if you built them. What's quite interesting is that if you conquer an AI, raze their cities and don't settle the space, the roads still function and are free of upkeep for you. If the roads are in your territory, or you built them, you can remove them with workers.

What I want to know is why there's always a +0.01 gold per trade route above the pop*1.25 value. It's bizarre and smells of very poor floating point rounding.

Thanks !

Stunningly helpful.

Its a bloopin shame they didn't bother to include a real Civolopedia and save you the work.

omglazers said:

Stunningly helpful.

Its a bloopin shame they didn't bother to include a real Civolopedia and save you the work.

Click to expand...

Agreed. Thanks Daniel D!

And it's a bloopin shame they didn't bother to include a real Civilopedia right from the start menu so you didn't have to load a game to access it.

Thank you for the information!

It makes the early tech decision clearer.

This is really situational but something fun to keep in mind...

By industrial age, if you unlock Order and Trade social policy for +5 and +3 hammer to all cities and all coastal cities respectively, another consideration for buying harbor asap in new coastal city is that those two policies scale pretty well with 50% railroad production buff, giving you wooping 12 hammers for population 1 city. And then those 12 hammers can be used to bulid stuff faster on your new town.

Again, extremly situational, but cool deal imo.