Transaction Fees are not a percentage of BTC transferred. For an ordinary transaction, the fee is the sum of spent inputs minus all outputs, including change; the miner may claim it in coinbase.
An input of 100,000 sat, payment of 60,000 sat and change of 38,000 sat yield a 2,000 sat fee. At 200 vB that is 10 sat/vB. BIP 141 virtual size is weight divided by four, rounded up. Input count and scripts can change size even for the same payment amount. [BIP 141: virtual size]
Wallets estimate rates from observed demand and confirmations. Miners select within rules and limited capacity; dependent transactions may be assessed as a package. A higher rate improves economic competitiveness but guarantees no time. An exchange withdrawal charge may also include the service’s own price. [Bitcoin Core v29.0: block assembly]
RBF offers a replacement sharing a spent input, subject to nodes’ replacement policy. CPFP spends an available parent output to raise the combined parent-child rate. Both require suitable authority, outputs and wallet support; neither universally accelerates someone else’s payment. [Bitcoin Core v29.0: replacement policy]
Fee rate × virtual size
A 140-vB transaction paying 12 sat/vB spends 1,680 sats in fees. Sending 0.001 BTC or 10 BTC with the same transaction structure does not change that calculation.
For the clearest picture, read this entry together with Transaction, Mempool, Mining, Block Subsidy, SegWit. The reverse links also lead from Mining, Transaction, Block Subsidy, Mempool.
01Are Bitcoin fees a percentage of the amount sent?+
No. Fees primarily depend on transaction virtual size and the fee rate needed for the desired confirmation time, not on the bitcoin value transferred.
02Can I increase a fee after sending?+
Often yes. Replace-by-fee can replace an eligible unconfirmed transaction, while child-pays-for-parent spends one of its outputs with enough combined fee to incentivize confirmation of the package.