Supply in Loss counts BTC whose current daily price sits below its realized cost basis. The output is expressed in BTC, so it measures the amount of underwater supply, not the percentage of supply and not unrealized loss in USD.
Expansion usually reflects market price falling through realized cost-basis bands. Contraction can come from spot recovery, lower on-chain repricing, or both, as coins move back above their last on-chain acquisition price. Supply in Profit and NUPL provide the closest context.
The metric does not show loss depth or selling pressure. It only states how much outstanding supply sits below cost basis. Realized Loss belongs to the spent-output layer, where losses are locked in through actual on-chain spending.
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