A crypto transaction in one sentence
A crypto transaction is a small piece of digitally signed data that tells a public blockchain to update its state — usually by moving coins from one address to another, but it can also call a smart contract, deploy code or burn tokens. Nothing fancy is happening physically; you are publishing a signed instruction to a global database that thousands of computers verify before it sticks.
If you have only ever moved money inside one bank, the model is a bit different. There is no central server that knows your balance and updates a ledger when you click send. Instead, you broadcast a signed message; many validators independently agree it is valid; one of them includes it in the next block; and the whole network then accepts your new balance. The bank, in this picture, is the entire network.
How a transaction actually works, step by step
Four steps cover every crypto transaction you will ever make, on Bitcoin, Ethereum or anything else.
1. You sign the transaction with your private key
Your wallet builds a transaction object — sender address, recipient address, amount, fee and a nonce — and asks you to sign it. The signing happens inside your wallet using your private key; the key itself never leaves the device. The output is a cryptographic signature that mathematically proves the holder of this key authorised this exact transaction. For a deeper look at how that keypair works, see our what is a private key guide.
2. The transaction enters the mempool
Your wallet broadcasts the signed transaction to its connected nodes, which gossip it to the rest of the network. Pending transactions live in the mempool — short for memory pool, basically a waiting room of unconfirmed transactions sorted by how much fee they pay. The mempool is not a single global queue; each node keeps its own copy, but in practice they look very similar within seconds.
3. A validator includes it in a block
Every few seconds on Ethereum, or roughly every ten minutes on Bitcoin, a validator builds the next block. They pick transactions from the mempool — typically the highest-fee ones first, because that maximises their reward — and bundle them into a block. When the block is added to the chain, your transaction is confirmed for the first time.
4. Confirmations stack up
One confirmation is good, but more confirmations are better. Each additional block on top of yours makes a chain reorganisation exponentially harder. For small payments, one confirmation is enough; for exchange deposits, six on Bitcoin or twelve to thirty on Ethereum is the typical norm. Once you are deep enough in the chain, reverting your transaction would require an attack so expensive that nobody would attempt it for the value at stake.
The three things every transaction carries
Strip away the format details and any transaction is just three numbers.
The input — where the value comes from
On Bitcoin this is one or more UTXOs, unspent transaction outputs you control — earlier transactions whose outputs are still unspent and tied to your address. On Ethereum it is just your account balance minus the amount you are sending. Either way, the input must cover the output plus the fee.
The output — where it goes
One or more recipient addresses with amounts. If your input is larger than what you are sending, the wallet quietly sends the change back to a new address it controls on Bitcoin, or just subtracts on Ethereum. Outputs can also be smart-contract calls — send a small amount of ETH to this contract and trigger this function — which is how DeFi swaps, NFT mints and most non-payment activity actually work.
The fee — what validators take to do the work
Every transaction pays a small fee to the validator who includes it. The fee is the bid you pay to compete for limited block space. When the network is calm, fees are tiny — a few cents on BTC, fractions of a cent on most L2s. When the network is busy, fees can climb to many dollars because everyone is bidding for the same scarce space. See our what is a gas fee guide for the full picture on Ethereum specifically.
Why fees vary so much
This is the part that confuses newcomers the most. Why does the same small transfer cost a few cents one day and many dollars the next?
The answer is block space. Each block can hold only so much data. When demand is low — a quiet Sunday morning — there is plenty of room and validators happily include low-fee transactions. When demand is high — a major airdrop, a stablecoin depeg, a popular NFT mint — the mempool overflows with people offering high fees to get in first, and you either bid up or wait.
Bitcoin and Ethereum handle this slightly differently. Bitcoin runs a pure first-price auction: you bid a fee, validators pick the highest bids. Ethereum uses EIP-1559, which sets a base fee that adjusts up or down based on congestion and burns it, then layers a small priority tip on top for the validator. Either way, the underlying logic is the same — limited space, market price.
What confirmed really means
People throw the word confirmed around loosely. It is worth being precise.
Confirmed technically means included in a block that is now part of the chain. But block ordering can change in the short term — two validators might briefly publish competing blocks, and one of them gets orphaned. The deeper your transaction sits, the less likely a reorganisation becomes.
For everyday use:
- 0 confirmations — broadcast but not yet in a block. Trust at your own risk.
- 1 confirmation — included in the most recent block. Enough for a coffee.
- 3 to 6 confirmations — solid for moderate value. Most exchanges credit Bitcoin deposits at six.
- 12 or more confirmations — effectively final for any realistic threat model.
On chains that use deterministic finality, the concept is a bit different — once a slot is finalised, it cannot be reverted at all without a coordinated attack on more than a third of validators. But the practical advice is the same: more time on chain equals more safety.
Bitcoin vs Ethereum transactions: two different models
Both chains do the same job, but the way they represent transactions differs.
Bitcoin uses the UTXO model. Your balance is the sum of unspent transaction outputs assigned to your address. Every transaction consumes one or more UTXOs entirely and produces new ones — like physical coins; you cannot break a banknote, you just spend it and get change. This is great for privacy techniques and for parallel validation but feels foreign to people used to bank accounts.
Ethereum uses the account model. Your address has a single balance number, just like a bank account. Sending ETH simply decrements your balance and increments theirs. This is more intuitive and makes smart contracts straightforward — a contract is just another account with code attached. The tradeoff is that account-model chains generally need stricter ordering, which costs some throughput.
Most other chains pick one of these two patterns. Solana, Cardano and a few others use UTXO variants; almost everything in the EVM family — Polygon, Arbitrum, Base, BNB Chain — uses the account model.
What can go wrong
Transactions are normally boring and reliable. But a few failure modes are worth knowing about.
You sent it to the wrong address. There is no undo button. If the address is a real one but not yours, the only path is asking the recipient nicely. If the address is invalid for that chain, your funds are gone forever. Always paste, verify the first and last few characters and send a small test for new addresses.
You picked too low a fee. Your transaction sits in the mempool, ignored. After some hours most nodes drop it and it disappears. You can usually speed it up by broadcasting a higher-fee replacement.
The transaction failed but you still paid gas. On Ethereum and EVM chains, if your smart-contract call runs out of gas or hits a revert, the transaction is still included in a block and you still pay for the work the network did — but the state change is rolled back. Failed swaps and reverting mints are common during busy periods.
Wrong chain. Sending a token on one network to an address that only listens on another network will not just work — the deposit will not arrive. Most exchanges can recover this with support, some cannot. Verify the network every time.
Tracking the news that moves transaction costs
Transaction fees and confirmation times are not abstract. Fees blow up because of news — a major exchange listing, a meme-coin frenzy, an outage that pushes activity back onto a slower layer, a halving narrative. Sentiment shifts can flip a quiet mempool into a forty-dollar-per-swap afternoon. Zippfeed surfaces the headlines that matter with a sentiment score (bullish, neutral or bearish) and an importance rating, so you can tell the difference between a real catalyst and noise before you click confirm. This is education, not financial advice — but knowing why fees are rising is half the battle of timing them.
