Bitcoin fees and confirmation times explained
Calculate a fee in sat/vB, see why transaction size matters and choose a confirmation target without treating it as a guarantee.
The quick answer
An on-chain fee pays for transaction space. The fee rate is measured in satoshis per virtual byte, or sat/vB. It is not a percentage of the bitcoin amount you send.
Rate and size determine the fee
A transaction spends inputs and creates outputs, often including change. More inputs can make it larger. Block-space competition affects the useful fee rate, while mining randomness affects how soon another block arrives.
Step by step
- 1
Check current conditions
Look at current fee estimates and the mempool. Choose a target that matches your urgency. A next-block estimate is a forecast, not a reservation.
- 2
Read your wallet’s preview
Check its estimated virtual size and total fee. A simple payment might be around 140 vB, but your actual transaction can be larger or smaller.
- 3
Keep a way to adjust
Check whether the wallet supports fee bumping before sending. If you can wait, avoid paying extra only because a previous block took longer than ten minutes.
Worked example
At 5 sat/vB, a 140-vB transaction costs 700 sats: 5 × 140. A 280-vB transaction at the same rate costs 1,400 sats, even if it sends less BTC.
Before you continue
A related question
Does paying more guarantee a faster confirmation?
No. It can improve priority relative to competing transactions, but new higher-fee payments, relay policies and unpredictable block times can change the outcome.
Try it with a tool
Sources & further reading
Source links checked on 15 Oct 2026. Examples explain the mechanics; provider fees and features can change.
- BIP 141 github.com
- Bitcoin.org bitcoin.org
