To calculate expected rewards from mining, we can do the following. First, calculate what percentage of total hashing power you command. To look up the network mining speed, execute the getmininginfo command in the console of the Bitcoin Core wallet. We will do our calculations with a GPU that can hash at 1 GH/s = 0.1 TH/s. If the Bitcoin network hashes at 400,000 TH/s, then our proportion of the hashing power is:
0.1 / 400 000 = 0.00000025 of the total mining power
On average, a Bitcoin block is found every 10 minutes; it amounts to six per hour and 144 for a 24-hour period. The current reward per block is 25 BTC; therefore, in a day we have 144*25 = 3600 BTC mined.
If we command a certain percentage of the mining power, then on average we should earn that proportion of the newly minted bitcoins.
Multiplying our portion of hashing power by the number of bitcoins minted daily we arrive at:
0.00000025 * 3600 BTC = 0.0009 BTC
As we can see, this is less than $0.25 USD...
