In Europa Universalis II, trading income is a form of monthly income generated by merchants in centers of trade. Each center of trade can hold up to 20 merchants at a time; a given country may have from zero to six merchants in a center of trade.
Each center of trade has a trade value, in ducats, which is the sum of the generated trade in all provinces which are part of the center of trade's trading area. The trade value of the center of trade is shown on the center of trade screen, and also on the main map when it is in trading map mode. Although trading income is computed monthly, the displayed trade value is the yearly figure that would be generated if everything stayed as it currently is at the time. The monthly amount of trade is the displayed figure divided by 12.
The trade value of each center of trade is divided into twenty shares, which are paid monthly to countries with merchants present in the center of trade. Each merchant takes one "slot". Each slot controlled by a country gets it one share. Thus, country with five merchants gets 1/4 (5/20) of the total trading income. A country with 6 merchants has the monopoly in that center of trade, and gets six shares for the six slots it controls, plus the shares for all empty slots. If no country has a monopoly, then nobody gets the income for any empty slots.
Thus, here is a formula for the trading income for country X from a center of trade Y:
- trading_income(X,Y) = trade_efficiency(X) * #shares(X,Y) * net_generated_trade(Y) / 240