Even a 6.5% Bitcoin Difficulty Cut Leaves S19 Rigs Underwater at 5-Cent Power

Bitcoin's mining difficulty is projected to fall by 6.5% at the next retarget, which would lift expected revenue per unit of hashing work by roughly 7% — yet the calculation still leaves Bitmain's older S19 machines earning less than their electricity cost at an illustrative tariff of 5 cents per kilowatt-hour. The scenario, built on November 9 inputs, isolates the retarget's arithmetic and nothing else; it holds Bitcoin's price, the block subsidy and average fees constant.

The mechanics are simple. Difficulty adjusts every 2,016 blocks, using block timestamps to target roughly a two-week cycle. Lower difficulty raises the probability that a given amount of computing work earns a block reward, so expected revenue per unit of work moves inversely with difficulty when reward value stays fixed. The scenario divides $31.89 by 0.935 — the share of difficulty remaining after a 6.5% cut — producing a 7% increase in expected receipts.

Both the November 13 date and the size of the cut remain estimates that can change as more blocks arrive. The figure also excludes what miners actually care about: pool fees, cooling and site loads, repairs, labor, hosting overhead, financing and equipment costs. The headline number is a ceiling, not a margin.

What do the machine-level numbers show?

The operating test used here is the highest electricity tariff that gross mining revenue can cover. Dividing expected daily receipts by a machine's daily wall-power consumption yields that electricity-only ceiling; a tariff above the ceiling means the machine's power draw alone exceeds gross revenue.

BITMAIN's specifications list two S19 variants — the 240-Ca models at 95 and 90 terahashes per second — each drawing a nominal 3,250 watts at 25 degrees Celsius. The S21 specification lists 200 TH/s at 3,500 watts under the same condition. The calculations assume continuous operation at nominal ratings and the 6.5% difficulty cut.

• At 5 cents/kWh, both S19 variants would still earn less than their electricity bill after the cut.
• A nominal S21 paying 8 cents/kWh would move from below to just above electricity coverage, leaving a cushion of about 10 cents a day before any other costs.

Both tariffs are illustrative. Ten cents a day is roughly $36 a year — enough, perhaps, to cover a repair, not a business.

How reliable are the assumptions?

The comparison uses each model's stated power and hashrate, but actual machines differ. BITMAIN gives the S19 variants a hashrate tolerance of plus or minus 3% and wall-power tolerance of plus or minus 5%. The S21 specification provides no numeric tolerance at all, which limits how precisely that thin cushion can be trusted. Each ceiling applies only to the specific model and nominal settings shown.

Earlier work pointed in opposite directions. CryptoSlate's October 14 analysis modeled the electricity squeeze from a projected difficulty increase, while its November 4 report examined a forward market implying little additional mining competition. The difficulty projection now sits on the easier side of that divide.

The next test is the completed adjustment and the hashprice that follows it. Whether the projected cut produces a viable operating margin depends on the actual revenue rate, equipment performance and every cost beyond the machine's power draw — none of which the scenario measures.