On the PrimeBit platform, you can trade linear perpetual contracts for Bitcoin, Ethereum and Litecoin. Once you find a partner for an exchange your income has a fixed value.
Whenever the price of the asset (Bitcoin, Litecoin or Ethereum) goes up or down $1, the value of your account changes by 0.1 mBTC (0.0001 BTC) per every single contract.
There is no expiration date for PrimeBit contracts. Instead, funding payments are exchanged between contract parties.