Bitcoin transaction fees explained
Learn how Bitcoin transaction fees work. Understand sat/vB, transaction weight, the mempool, confirmation targets, RBF, CPFP and fee estimation.
A Bitcoin transaction fee is the difference between the bitcoin a transaction spends and the bitcoin it sends out. Fees help miners decide which transactions to include when block space is limited.
Fees are usually compared in satoshis per virtual byte, written as sat/vB. A satoshi is the smallest unit of bitcoin. A virtual byte is a way to measure the weight of a transaction.
Fee rate and total fee are different
The fee rate is not the total fee. A transaction with a larger virtual size needs a larger total fee to pay the same fee rate.
A simplified calculation is:
total fee = fee rate × virtual size
For example, a transaction that is 200 vB at 10 sat/vB would pay 2,000 satoshis. This is an illustration, not a live fee quote. Actual transaction size depends on the inputs and outputs involved.
Why Bitcoin fees change
Bitcoin blocks have limited space. When more transactions compete for that space, miners can prefer transactions with higher fee rates. A wallet or fee estimator can suggest a rate for a chosen confirmation target, but it cannot guarantee when a transaction will confirm.
Use a current fee estimator when preparing a transaction. An article cannot provide a reliable fixed fee because network conditions change.
If a transaction is waiting
Some transactions can be fee-bumped after broadcast.
Replace-by-fee, or RBF, can replace an earlier transaction with a higher-fee version. Child-pays-for-parent, or CPFP, can use a later dependent transaction to add an incentive for both transactions to be confirmed together.
These methods depend on the wallet, the transaction and network policy. Check what your wallet supports before sending.
Use block space carefully
Modern Bitcoin address formats can reduce transaction weight in many cases. Services that send many payments may also use batching. These approaches can reduce block-space use, but the result depends on the transaction itself.
Before sending bitcoin, check the destination address carefully. Then review the fee rate, total fee and confirmation target separately.
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