The life of a transaction

You’ve built a transaction and signed it. Now you hit “send.” What happens next isn’t instant magic — it’s a short, well-defined journey: your payment is broadcast to the network, waits its turn, gets mined into a block, and is then buried deeper and deeper until reversing it would cost more than the world could spend. Let’s follow it.

1. Broadcast — into the mempool

Your wallet hands the signed transaction to a few nodes it’s connected to. Each one checks it’s valid (good signatures, no double-spend, follows the rules) and, if so, relays it to its own peers — so within a couple of seconds your transaction is rippling across the whole network. Every node keeps these unconfirmed transactions in its mempool (memory pool): a waiting room of payments that are valid but not yet in a block. At this point your payment is a broadcast promise — real and visible, but not yet settled.

2. The fee market — an auction for block space

A new block arrives only about every ten minutes, and each block holds just a few thousand transactions. When more people want to transact than the next block can fit, getting in becomes an auction. You attach a fee, quoted as a rate — satoshis per virtual byte (sat/vB) — and miners, naturally, fill their limited space with the highest-paying transactions first.

• Quiet network? A minimal fee confirms quickly and costs pennies.
• Congested network? Fees rise as everyone bids for the same scarce space.
• Stuck with too low a fee? You’re not trapped — “replace-by-fee” (RBF) lets you rebroadcast the same payment with a higher fee, and “child-pays-for-parent” (CPFP) lets a follow-up spend drag a cheap parent along.

Crucially, no one sets these fees. There is no company deciding what a transaction costs — it’s a live, open market between everyone who wants to use the next block.

Try being a bidder. Set your fee rate and watch whether your transaction claims a spot in the next block or waits behind higher-paying ones. Add congestion to fill the mempool, and mine a block to clear the top bidders.

3. Confirmation — buried in proof of work

When a miner includes your transaction in a block, that’s one confirmation. Each new block mined on top of it is another. Why do people wait for a few? Because to reverse a confirmed transaction, an attacker would have to secretly re-mine that block and every block after it faster than the entire honest network is extending the real chain — exactly the impossible race from the Proof of Work lesson. Every block deeper makes that race exponentially more hopeless.

So confirmations are a dial you set against value at risk: for a coffee, zero or one confirmation is fine; for a house, wait for several. There’s no bank to phone and no chargeback — a deeply confirmed Bitcoin payment is simply final.

Slide the confirmations up and watch your transaction get buried — each block one an attacker would have to secretly out-mine the whole network to undo.

4. Who collects your fee? The coinbase

The miner who finds the block claims every fee inside it — plus the block subsidy of newly minted bitcoin — in a special first transaction called the coinbase (no relation to the company). That single transaction is how brand-new coins are born and how fees pay for the security that protects everyone. As the subsidy halves toward zero over the coming century, those transaction fees gradually become the miners’ main reward — the network’s security budget shifting smoothly from issuance to fees.

You’ve now seen the whole machine work end to end — from a signed transaction, through the mempool and the fee market, to an irreversible payment set in proof of work. The next two lessons step back to name what we’ve built — its defining properties — and weigh it honestly against gold, fiat and other assets.

Key takeaways

• A broadcast transaction waits in nodes’ mempools until a miner includes it in a block; block space is limited, so fees (sat/vB) act as an open auction for the next block.
• Each block mined on top adds a confirmation; reversing a confirmed transaction means out-mining the whole network, so depth = finality. The miner collects the fees plus the block subsidy in the coinbase transaction.

Check yourself

Why do transaction fees rise when the network is busy?

A company raises themBlock space is limited, so users bid for the next blockMiners vote on feesThe blockchain slows down

What does waiting for more confirmations give you?

A faster refundGreater finality — reversing it would mean out-mining the whole networkA lower feeMore privacy