Tax is the fundamental source of financial income in Galactic Civilizations II. The amount of tax revenue is largely determined by how large your population is and how high your tax rate is set. Increasing the tax rate will increase your tax revenue at the expense of decreasing your approval rating on your planets. Tax revenue can also be affected by Racial bonuses, Planetary improvements, government type, your political party, amount of money in the treasury and game version ("Dark Avatar" gives 40% less money than "Dread Lords"). The income from a planet is given by the formula:
constant * sqrt(population_in_billions) * tax_rate * (1 + (sum from buildings on planet)) * (1 + (sum from racial bonuses/maluses) )
Constant seems to be:
- - 34.5 in Dread Lords
- - 28.5 in Dark Avatar before ver. 1.6
- - 24.0 in Dark Avatar after ver. 1.6, up to current 1.8
- - 20.0 in DA and for planets over 25B pop
- - about 20.0 or a little less in 2.04 for all planet
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- Notes
- See discussion tab for a formula explanation.
- There seems to be a small penalty to tax revenue (up to ~4%) for low approval (below about 50%)
The first point of tax (1% tax rate) decreases the approval rating on all of your planets by 1%. Each point of tax rate after that decreases your approval by slightly more (the UI will only show you whole percentages so you will see mostly 1% change for a while, then a 2% every so often and eventually 2% most of the time and 1% some of the time as you approach 100% tax rate).
Periodically, there are sudden out of the ordinary leaps in approval loss per tax rate increase. Below are listed all of them up to 81% where a giant leap occurs and there is no reason you would ever set your tax rate this high (unless you were OK with 0% approval, in which case you might as well set it to 100% tax rate).
| Tax Rate (%) | Approval Change (-%) |
| 40 | 5 |
| 50 | 5 |
| 60 | 5 |
| 70 | 10 |
| 81 | 180 |