How Bitcoin works.
The protocol in plain English.

READ4 min · UPDATED2026-05-01

Reviewed against primary sources cited at the bottom of this page.

A six-minute explanation of how Bitcoin transactions, mining, the blockchain, and the 21 million cap fit together. No jargon. No "magic internet money" hand-waves. The protocol is genuinely simple at the level you need to understand it as a user.

READING TIME: ~6 MIN

THE SHORT VERSION

Bitcoin is a shared spreadsheet of who owns what. About every 10 minutes, computers around the world race to solve a costly puzzle for the right to add the next page of transactions to the spreadsheet. The winner gets paid in newly created Bitcoin. The puzzle is so expensive to solve that rewriting old pages is economically infeasible. New Bitcoin is created on a fixed schedule that ends at 21 million coins. That's the whole protocol at the level a normal user needs.

How transactions work

A Bitcoin "wallet" is not a place where coins are kept. It is software that holds two things: private keys (cryptographic secrets that prove you own coins assigned to specific addresses) and a list of those addresses. To send Bitcoin, your wallet creates a transaction message that says "the coins at address A are now assigned to address B" and signs it with your private key. The signature is mathematically verifiable by anyone but cannot be forged without the key.

Your wallet broadcasts the transaction to the network. Mining nodes pick it up, verify the signature, and include it in the next block they mine. Once your transaction is in a block, and a few more blocks have been added on top, it is irreversible.

Proof of work, in plain English

Miners compete to add the next block to the chain. To win, a miner has to find a number (a "nonce") that, when combined with the block contents and run through a one-way hash function, produces an output below a target value. There is no shortcut. Miners just guess, trillions of guesses per second, until one of them finds a winning number. The winner broadcasts the new block, claims the block reward in newly created Bitcoin, and the race for the next block begins.

Why this matters: rewriting an old block requires re-doing all the proof of work for that block plus every block after it, faster than the rest of the network is producing new blocks on top. The deeper a transaction sits in the chain, the more compute would be required to reverse it. Six confirmations (about an hour) is the standard threshold for "settled" because the cost of reversal at that depth is prohibitive even for state-level adversaries. Detail at Proof of Work.

The blockchain

"Blockchain" is the data structure: a chain of blocks where each block references the cryptographic hash of the previous block. Change anything in any block and every block after it has to be re-mined. The Bitcoin blockchain is currently around 600 GB on disk and grows by roughly 1 MB every 10 minutes. Anyone can download the entire history and verify it independently. Around 16,000 to 20,000 nodes worldwide do exactly that verify×DON'T TRUST, VERIFYClaim: The Bitcoin reachable-node count fluctuates between roughly 16,000 and 20,000 worldwide.Verify at: Bitnodes live count ↗Bitnodes counts only reachable nodes. The total node count including non-listening nodes is higher..

Mining and network security

Miners are paid in two ways: a "block subsidy" of newly created Bitcoin (3.125 BTC per block as of the 2024 halving) plus the transaction fees from the transactions in the block. The block subsidy halves every 210,000 blocks (roughly every 4 years). It started at 50 BTC per block in 2009; it will halve to 1.5625 BTC in 2028 and continue halving until it rounds to zero around 2140.

As the subsidy shrinks, transaction fees become the dominant compensation for miners. Whether the fee market alone can sustain network security is an open empirical question that the protocol's long arc will answer. So far, fee revenue has scaled with usage and price; whether that scaling continues is part of the bull case and part of the bear case.

The 21 million cap and halvings

The supply schedule is fixed in code verify×DON'T TRUST, VERIFYClaim: The Bitcoin protocol caps total supply at 21 million coins via a halving schedule.Verify at: Nakamoto (2008) Bitcoin whitepaper ↗The cap is enforced by consensus rules in the reference implementation; changing it would require a hard fork rejected by economic majority.:

2009 to 2012: 50 BTC per block (~25 minutes worth of issuance per coin in a sense; 7,200 BTC per day).
2012 to 2016: 25 BTC per block.
2016 to 2020: 12.5 BTC per block.
2020 to 2024: 6.25 BTC per block.
2024 to 2028: 3.125 BTC per block.
2028 to 2032: 1.5625 BTC per block. And so on.

The total approaches 21 million asymptotically and rounds to that figure around 2140. Approximately 19.7 million coins are already in circulation. About 94% of all Bitcoin that will ever exist has already been mined.

No central party can change the cap. Changing it would require a hard fork that the economic majority of the network rejects. Bitcoin holders, exchanges, miners, and node operators have repeatedly demonstrated they will reject changes to monetary policy. The cap is as immutable as anything in software can be.

What this changes for tomorrow

If you understand transactions and proof of work, the rest of the Bitcoin learning curve is incremental. Most "advanced" topics build on these primitives.
Self-custody starts with understanding that owning Bitcoin = owning the private keys. Without the keys, you have a claim on a custodian, not the asset. Detail at Bitcoin Security.
The fact that no central party can change supply is the structural property the entire investment case rests on. Detail at Why Bitcoin.

Continue the sequence

→ Bitcoin Security, self-custody and seed phrases · 7 min → Proof of Work, the deep dive on mining and energy → Why Bitcoin, the case for the design → Bitcoin for Beginners, the full long-form intro

Last updated 2026-05-01. Not financial advice.

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