Bitcoin mining profitability comes down to one number more than any other: your electricity cost per kilowatt-hour. Hardware and difficulty matter, but power is the bill you pay every single day.

The math: daily cost = miner power draw (kW) × 24 × your $/kWh rate. An S21 at 3.5kW on $0.10/kWh costs $8.40/day to run. Compare that against daily revenue at current difficulty and price.

Rough breakevens in 2026: under $0.06/kWh is comfortable, $0.06–0.10 is marginal and depends on BTC price, and above $0.12 is nearly impossible for home miners without free cooling.

Do not forget the hidden costs: heat (it has to go somewhere), noise, hardware depreciation, and pool fees of 1–3%. Run the full calculation before buying a single ASIC.