What Is Bitcoin?

What is Bitcoin? It is a form of digital money that exists only as entries on a public ledger, maintained by thousands of computers that follow the same open-source rules. Nobody needs permission to use it, no company runs it, and no central bank can print more of it. This guide explains how those rules work, what the famous supply cap and halvings mean, and what the risks are for anyone thinking of owning some.

What is Bitcoin and where did it come from?

Bitcoin was described in a 2008 paper published under the name Satoshi Nakamoto, and the network began running in January 2009. The goal was a way to send value directly between people online without relying on a bank to keep the records. The identity of Satoshi Nakamoto has never been confirmed.

The word is used in two ways: "Bitcoin" for the network and its rules, and "bitcoin" (or BTC) for the units that move on it. Each bitcoin divides into 100 million smaller units called satoshis, or sats, so nobody needs to buy a whole coin. At an illustrative price of $62,500, $50 buys 0.0008 BTC, which is 80,000 sats.

How the network works

Every Bitcoin transaction is broadcast to the network and collected by miners. Miners bundle transactions into a block and compete to find a number that makes the block's cryptographic fingerprint meet a difficulty target. This is proof of work: finding the answer takes enormous computing effort, but checking it is instant. The winner adds the block to the chain and is paid in new bitcoin plus the fees attached to the transactions.

The difficulty adjusts automatically so that a new block appears roughly every ten minutes, whatever the amount of computing power in the network. Each block links to the one before, so rewriting history would mean redoing all the work since that point faster than the rest of the network, which is why settled transactions are treated as final.

Anyone can run a node, a computer that stores the ledger and checks every block against the rules. Nodes reject blocks that break the rules, such as ones that create too many coins, which is what keeps miners honest.

The 21 million cap and halvings

Bitcoin's rules limit total supply to 21 million coins. New coins enter circulation only as block rewards, and the reward is cut in half every 210,000 blocks, roughly every four years. These events are called halvings.

With about 144 blocks a day (six an hour for 24 hours), the current reward adds roughly 450 new bitcoin daily. Each halving cuts that flow in half. Over time, miners are expected to rely more on transaction fees as the block reward shrinks towards zero.

Halvings are often described as bullish events, but a lower flow of new coins does not guarantee a higher price: the schedule is public and known years in advance, and price still depends on demand.

Wallets and ownership

Owning bitcoin means controlling the private key that can sign transactions for a particular address. You can hold the key yourself in a software or hardware wallet, or let a platform hold it for you. Holding your own key removes the risk of a platform failing but makes you fully responsible for backups and security. Leaving coins on a platform is simpler but means trusting that firm. Either way, transactions cannot be reversed, and a lost key usually means lost coins. The crypto guide covers custody in more depth.

Some countries also allow exchange-traded products that track the bitcoin price, held in an ordinary investment account. These remove the need to manage keys but add fees and their own structural risks, and availability depends on local rules.

What sets the price

Bitcoin produces no earnings, pays no interest and has no issuer promising to buy it back. Its price is simply the latest point at which buyers and sellers agree. Supporters point to its fixed supply, its independence from governments and its track record of running for many years without the ledger being rewritten. Critics point to its lack of cash flows, its energy use and its role in scams and ransomware. Both views move the price, alongside interest rates, investor flows, leverage in the derivatives market, regulation and headlines.

The result has been extreme volatility. Bitcoin has risen many times over in some periods and has lost well over half of its value in others, sometimes within months. Anyone holding it should expect that pattern to continue and size their position so that a very large fall would not change their plans.

A note on fees and costs

Buying through a platform involves a trading fee or spread, and moving coins on-chain involves a network fee that rises when the network is busy. For small, frequent purchases these costs can take a meaningful share of the amount invested. Our crypto profit calculator shows the effect of a fee on both the buy and the sell.

Common misconceptions

• "Bitcoin is anonymous." Every transaction is public and permanent. Addresses are not names, but analysis firms and authorities regularly link them to people, especially where platforms have collected identity documents.
• "The cap means the price must rise." Scarcity only supports a price if demand holds up. A fixed supply meeting falling demand produces falling prices.
• "Bitcoin cannot be hacked, so my coins are safe." The network's ledger has proved robust, but wallets, platforms and people are hacked or tricked routinely. Most losses happen there.
• "You need a whole coin." Fractions down to one hundred-millionth of a bitcoin can be bought and sent.

Risks to weigh

• Price risk: large, fast falls are common and there is no floor.
• Custody risk: platform failures, hacks, lost keys and phishing.
• Regulatory risk: rules on platforms, taxes and products change between countries and over time.
• Scam risk: Bitcoin is the payment of choice for many frauds, from fake investment platforms to blackmail emails; see how to spot trading scams.
• Behavioural risk: round-the-clock trading and constant headlines make it easy to buy after rises and sell after falls.

Where Bitcoin fits for a long-term investor

For people building wealth over decades, the honest answer is that Bitcoin is a speculative asset whose long-run role is still debated. Some investors choose to hold a small amount they can afford to lose entirely; many choose to hold none. What matters is that the decision is made with an understanding of the mechanics above, not in response to a price chart or a friend's success. To compare it with other tokens, read our guide to comparing cryptocurrencies, and to understand the dollar-pegged tokens it trades against, see USDT explained.

Sources

• Bitcoin white paper (Satoshi Nakamoto, 2008)
• Bitcoin Core developer documentation: block reward schedule and difficulty adjustment