Why Mining Cost Is Bitcoin's Hardest Bottom Anchor: The Marginal Miner

Quick answer: When Bitcoin's price falls, older rigs shut down first (their power bills exceed output), and network hashrate consolidates onto the most efficient machines — so what actually supports price is not the "average cost" but the all-in cost of the latest-generation miner. Price below that means even the most efficient miners lose money; that exact condition marked the Mar-2020 and Nov-2022 bottoms. The BTC Cycle Thermometer uses this price-to-latest-rig-cost ratio as its 20% fundamental anchor — the largest single weight.

The marginal-miner logic

Mining is perfectly competitive commodity production: the product is identical, cost is electricity. As price falls, older rigs hit their shutdown price and exit, difficulty adjusts down, and the survivors — running the most efficient hardware — keep producing at lower cost. The process keeps pushing the effective cost line toward the newest rig: the last miner standing always runs the most efficient machine. Fleet-average efficiency therefore systematically overstates support, because the average includes rigs that should already be off.

The formula

Network hashrate (live from mempool.space) × latest-rig efficiency (auto-fetched daily from miner databases, currently ~9-10 J/TH class) × 24h ÷ 1000 = daily network power; × electricity ($0.06/kWh assumption) ÷ daily issuance (144 blocks × 3.125 BTC × 1.04 fees) = electric cost (shutdown price); × 1.55 (depreciation + opex) = all-in cost. Every assumption is disclosed on the tool page; plug your own numbers into the mining calculator to verify.

Two historical tests

March 2020: the COVID crash pushed price through the then-newest rig's all-in cost; miners capitulated, hashrate plunged — and price rose over 10x in the following year. November 2022: the FTX collapse drove price below the S19 XP-class cost zone; listed miners dumped BTC to survive — that was the cycle low. Common to both: price spent very little time below the latest rig's cost, because supply-side self-correction (shutdowns → difficulty down → cost down) restores balance fast.

When it fails

Three caveats: structural power-price shifts (e.g. large negative-price mining) move the line; a generational efficiency jump can drop the anchor 30% overnight — which is exactly why the thermometer auto-updates the rig model daily; and in extreme liquidity crises price can briefly ignore any cost. It is the hardest anchor, not an unbreakable floor — inside the thermometer it cross-checks against the other eight indicators rather than ruling alone.