The Budget page is where you can see an overview of your nation's income and expenses. Incomes and Expenses are calculated every hour, and will freeze after 120 hours (5 Days).
Working population is determined by a nation's population and unemployment rate. The amount of unemployed citizens (determined by the unemployment rate) is deducted from the nation's total population, resulting in the Working Population.
Average income is determined by a nation's average happiness. This is the current formula (Updated 6/7/2012)
Average Income = (0.5 + National Happiness * 0.5) + National Events
A Nation's overall tax revenue is determined by the average income, working population, and tax rate of a nation. The current formula is as follows (Updated 6/7/2012)
Tax Revenue = Tax Rate * Average Income * Working Population
Unlike Income, expenses are determined by a lot of factors, both domestic and military.
Domestic expenses are determined by population and zone types.
Infrastructure maintenance is determined by the total amount of Residential Zones a nation has. Each zone costs $300 + Residential/500 in maintenance.
Government costs are directly determined by population. Each citizen costs $0.0225 + Population/10,000,000,000. The Capitol Building Marvel reduces government costs by 2%.
Civil Services are directly determined by the amount of Civic Zones your nation has. Each zones costs $250 + Population/10,000,000,000 in upkeep.
Healthcare costs are directly determined by population. Each citizen costs $0.015 + Population/10,000,000,000.
Military expenses are determined by the amount of military units your nation has.
Ballistic Missile UpkeepEdit
Ballistic missiles cost $75,000 per missile owned to maintain.
Nuclear Weapon UpkeepEdit
Nuclear weapons cost $1,000,000-$20,000,000 per weapon owned to maintain, depending on how many you own.