When you go to opskins to sell, you can sell at "list price" or "cut price". "cut price" is either 10% or 5% less than "list price" because OPSkins takes that commision. Here is a picture of what I mean. Profit means overall profit after you've sold all your skins on OPSkins. Note that the profit is in skins value, not paypal cash value.
If you want to calculate the amount of money you make per skin in order to BREAK EVEN ($0 profit), fill in "deposited", "bonus", "quantity". The "Break Even Cut Price" will display the "your cut" price for each skin in order to break even, or in other words, make zero profit.
To calculate overall profit, you fill in "deposited", "bonus", "quantity", "Enter Cut Price". "Enter Cut Price" is the cut price you want to sell each skin at, and the output "Profit at Cut Price" is the amount of profit you'd make if all your skins sold at "enter cut price".
Note: This is assuming that you spend all of your "deposited money" and are only left with bonus money onsite.