PayJoin
PayJoin is a privacy technique where both sender and receiver contribute inputs to one transaction, breaking chain-analysis heuristics.
Chain-analysis firms rely on the 'common-input-ownership heuristic': if multiple inputs sit in one transaction, they're assumed to be from the same owner. PayJoin breaks that: the receiver also contributes an own input. To outsiders it looks like a normal payment, but the heuristic no longer holds — no-one knows which inputs and outputs belong to whom.
Example
Alice pays Bob 0.05 BTC. Bob's PayJoin wallet silently adds one of his own 0.02 BTC UTXOs as input and adjusts his output. The blockchain shows one tx with 2 inputs and 2 outputs — indistinguishable from a regular CoinJoin.
Frequently asked questions
Why should a merchant support PayJoin?
Three reasons: customer privacy, own UTXO consolidation (small UTXOs get consumed during payments), and defending the whole network against surveillance. BTCPay Server and Wasabi support PayJoin out of the box.
Related terms
Further reading
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