Basic formula: daily income in BTC = (your hashrate / network hashrate) × 144 blocks × 3.125 BTC (block reward). Convert the BTC result to fiat at the current rate: multiply by the BTC price in USD or your currency.
Net profitability is fiat income minus electricity (power in kW × 24 × tariff per kWh) and minus pool fee (already included if you use the calculator with fee). Use an up-to-date rate from an exchange or aggregator.
For comparing pools and devices it’s useful to compute “gross” and “net” daily income in USD or local currency (after electricity and pool fee).