How Bitcoin Mining Works

At its core, Bitcoin mining is how the network agrees on which transactions happened and in what order, without any central authority. Roughly every ten minutes the pending transactions are bundled into a 'block', and miners compete to be the one that gets to add that block to the chain. The winner is rewarded, and everyone else moves on to compete for the next block. This is the engine that both issues new bitcoin and keeps the ledger honest.

The competition itself is a guessing game built on hashing. A hash function takes any data and produces a fixed, random-looking output; change the input even slightly and the output changes completely. Miners repeatedly hash the block's data along with a changing number until they find an output below a certain target. There's no shortcut — you simply have to try enormous numbers of guesses, which is why miners run hardware that performs trillions of attempts per second.

This is what 'proof-of-work' means: finding a valid hash is hard and takes real energy, but verifying it is instant for everyone else. Because each block also references the one before it, changing an old transaction would mean redoing the work for that block and every block after it, faster than the rest of the network combined. That's effectively impossible at Bitcoin's scale, which is how proof-of-work secures the chain against tampering.

To keep blocks coming about every ten minutes regardless of how much mining power is online, the network adjusts the difficulty roughly every two weeks. If more miners join and blocks come too fast, difficulty rises; if miners leave, it falls. Separately, the block reward — the new bitcoin paid to the winning miner — halves roughly every four years in an event called the halving, steadily reducing new supply toward the fixed 21-million-coin cap.

Put together, mining does three jobs at once: it confirms transactions, releases new bitcoin on a predictable schedule, and secures the network by making attacks economically irrational. As the block reward shrinks through successive halvings, transaction fees are designed to make up a growing share of what miners earn, so the system can keep paying for security long after most new coins have been issued.