Sending bitcoin looks like sending a bank transfer: you type an address and an amount, tap send, and a moment later the other person sees it. Underneath, nothing works like a bank. There is no account with a balance, no company approving the payment and no way to reverse it. Understanding the four steps below is the fastest way to stop treating Bitcoin as magic and start using it safely.
Before we start: there are no balances, only coins
A bank keeps a number next to your name and moves it up and down. Bitcoin keeps no such number. What exists on the blockchain is a list of unspent outputs, usually shortened to UTXOs. Think of them as bills in a physical wallet: a bill of 0.3 BTC, another of 0.05 BTC, another of 0.12 BTC. Your “balance” is simply your wallet software adding up the bills it knows it can spend.
This has a consequence that surprises people: when you pay 0.1 BTC using a 0.3 BTC bill, the whole bill is spent. The transaction creates two new bills: 0.1 BTC for the recipient and the rest for you as change, sent to a fresh address your wallet controls. That is why a block explorer often shows two outputs on a payment you thought was a single transfer, and why your wallet quietly manages dozens of addresses.
Step 1 — Your wallet builds and signs the transaction
When you press send, your wallet performs three jobs locally, on your device, before anything reaches the internet:
- Select inputs. It picks which of your bills (UTXOs) to spend so that they cover the amount plus a fee. This is called coin selection; different wallets use different strategies.
- Write outputs. It lists who receives what: the recipient's address and amount, and a change output back to you if the inputs were larger than needed.
- Sign. It proves ownership of each input with your private key. The signature is mathematically tied to this exact transaction, so nobody can change the amounts or the destination and reuse the signature. The private key itself never leaves the device.
The result is a few hundred bytes of data. It contains no names, no account numbers and no password, only references to the coins being spent, the new outputs and the signatures.
Step 2 — The network checks it and holds it in the mempool
Your wallet hands the transaction to one or several nodes, computers running Bitcoin software. Each node independently verifies the transaction before passing it on: are the inputs real and still unspent? Do the signatures match? Are the outputs not larger than the inputs? Is the format valid? If any check fails the transaction is dropped on the spot; no fee is paid and nothing happens.
Valid transactions wait in every node's mempool, the memory pool of transactions that are known but not yet included in a block. At this point your recipient can already see the payment as unconfirmed. It is a promise, not a settlement: an unconfirmed transaction can, in some cases, be replaced or simply never confirm.
Why is there a fee, and who decides it?
Space in a block is limited, so transactions compete for it. The fee is not a percentage of the amount sent; it is paid per byte of data, quoted in satoshis per virtual byte (sat/vB). A tiny payment and a huge one can cost the same if they take the same space. When many people want to transact at once the going rate rises; on quiet days it falls. Your wallet estimates a rate; you can usually override it. Paying too little means waiting longer, sometimes days.
Step 3 — A miner puts it in a block
Miners gather transactions from their mempool, prefer the ones paying the highest fee rate, and race to find a block. Finding a block means repeatedly hashing a candidate until the result meets a difficulty target; on average the whole network succeeds about once every ten minutes. The winner broadcasts the block, every node verifies every transaction in it once more, and if all is well the block is added to the chain. Your transaction now has one confirmation.
The miner collects the fees of all included transactions plus the block subsidy, the newly created bitcoin. That reward is what pays for the enormous amount of computation that protects the ledger.
Step 4 — Confirmations make it final
A transaction with one confirmation is inside the newest block. Could that block be undone? In theory, yes: if another miner found a competing block at the same height and the network followed that branch instead, transactions in the abandoned block would return to the mempool. Such small reorganisations happen occasionally and resolve within a block or two.
Each additional block built on top of yours makes reversal exponentially more expensive, because an attacker would have to redo all that work faster than the honest network. That is why exchanges and merchants wait for several confirmations: six is the traditional threshold for large amounts, one or two is common for small ones, and zero (accepting an unconfirmed transaction) is only safe when the amount is small enough that fraud would not be worth the effort.
What can go wrong
The transaction is stuck
If your fee rate is below what miners currently accept, the transaction sits in mempools. Two standard fixes exist. With Replace-By-Fee (RBF) your wallet rebroadcasts the same payment with a higher fee, and miners take the better-paying version. With Child-Pays-For-Parent (CPFP) the recipient, or you via the change output, spends the unconfirmed coins in a second transaction with a generous fee; miners then include both together. Modern wallets expose at least one of these as a “speed up” button.
The address was wrong
There is no support desk. If the address belongs to someone else, they own the coins; if it belongs to nobody, the coins are gone. Addresses include a checksum, so a typo is almost always rejected by the wallet before sending, but a valid address that is not the one you meant, for example pasted by malware, passes every check. Always verify the first and last characters of the address on the receiving side before confirming.
You paid a fee on a “failed” payment
You did not. A transaction is either in a block, in which case the payment happened and the fee was earned, or it is not, in which case no fee was collected. Bitcoin does not charge for attempts.
Why it is designed this way
Every rule above serves one goal: letting strangers who do not trust each other agree on who owns what without a referee. Signatures replace identity checks. Independent verification by every node replaces a central approver. Proof-of-work and confirmations replace the bank's guarantee that a settled payment stays settled. The price of that design is that mistakes are yours to prevent, which is exactly why understanding the steps matters.
Frequently asked questions
How long does a Bitcoin transaction take? It reaches the network in seconds and is usually confirmed in the next block, about ten minutes on average, if the fee is competitive. Most services consider it final after several confirmations, so plan on roughly an hour for large amounts.
Can a Bitcoin transaction be cancelled or reversed? Not once it is confirmed. An unconfirmed transaction can sometimes be replaced with a higher-fee version, which is how wallets offer a “speed up” or, rarely, a “cancel” option, but there is no reversal mechanism and no one to appeal to.
Why does my transaction show two outputs when I sent one payment? Bitcoin spends whole coins (unspent outputs). If the coin you spent was bigger than the payment, the difference comes back to you as change in a second output, sent to a new address that your wallet controls.
Is the fee a percentage of the amount? No. Fees are paid per byte of transaction data, so a small and a large payment can cost the same. The rate depends on how busy the network is at that moment.