https://na.wargaming.net/support/en/products/wot/article/18956/#section_1

Payment for battle participation:

Payment for battle is a guaranteed amount of Credits, independent of the vehicle's performance in battle and proportional to the vehicle's Tier (the vehicle’s value in battle).

Payment for battle consists of X * vehicle-tier for defeat or a tie, and 1.85X * vehicle-Tier for victory.

Payment for inflicting damage to the enemy:

For every point of damage inflicted, the vehicle receives Y Credits independent of the Tier. You will get 0.1Y bonus Credits per Tier difference of the enemy, in comparison to yours (enemy vehicle Tier - yours = 0.1Y per Tier difference). Damage inflicted by fire is counted towards the player who set the fire. In case of an ammo rack explosion or other damage caused by the initial fire, all damage is counted towards the player who set it.

Damage is counted if inflicted upon the enemy. Damage by friendly fire is not counted. Unintentional kills (frag) are not individually counted towards the payment.

If you shoot a target spotted by another allied player, then you receive 0.5Y Credits for damage.

Payment for spotting:

For all initial spotting of enemy tanks, the player receives Z Credits, and 2 * Z for damaging SPGs.

Payment for base capture:

Base capture is paid out with a certain sum of Credits. The payment is independent of the number of vehicles and their Tiers - everyone in the circle receives equal payment. This only applies to successful base captures. Base captures that are interrupted will not earn you anything.

Balance coefficient is a factor for individual settings of a tank's profitability. Payment for all vehicles, except Premium, is multiplied by the coefficient W. The given coefficients for Premium vehicles are higher.

The average tank has an average coefficient of 0.65 - 0.71, except for Premium tanks which have 1.10-1.3 (information to be updated as of April 11th, 2011).

Premium Account:

For Premium accounts, Credits are multiplied by 1.5