Start with the input collections
For a standard ten-skin contract, each input contributes a share of the contract to its collection. The simulator divides that collection's share among its eligible skins at the next rarity grade. Adding another input from a collection changes the collection weight; it does not simply add one more possible result.
Why the displayed chance can change
Changing the input mix, rarity grade, or available output pool can change the odds. That is why the outcome list should be reviewed after editing a contract. The preview images do not change the configured outcome chances or the float formula.
Knife and glove contracts need extra caution
Covert-to-Gold contracts depend on the eligible case pools and configured finish or phase weights. Those special weights in this simulator are estimates, not an official Valve probability feed. Rare finishes such as Sapphire, Ruby, Emerald and Black Pearl can be highlighted, but a rare hit is not automatically a financial win.
Use odds together with value
A high-value skin with a very low chance may still leave the overall contract with a negative expected return. Compare the full outcome list, input cost and price coverage before deciding whether a contract is interesting. For the arithmetic, see the expected-value guide.