Proof of Work and Difficulty: Bitcoin's Very Fussy Lottery
Part of the guide: How Bitcoin works
Imagine a raffle where a computer prints a fresh ticket every time it tries. Most tickets lose. Keep trying until one lands below the posted limit, and you have a winner. Bitcoin mining is a lot like that, except the prize is a place in the next block. No tiny raffle drum required.
The 10-second version
- Proof of work is a costly-to-find, quick-to-check answer. Miners try block data and a changing number until its hash is below the network's target.
- Difficulty describes how hard that target makes the search. A lower target means fewer hashes qualify.
- The proof does not make a block automatically valid. Other nodes still check its transactions and rules.
The whitepaper describes scanning for a value whose hash starts with enough zero bits. It says the average work grows exponentially with the required zero bits, while checking a candidate takes one hash. The same rule can be described as finding a hash below a target. Bitcoin whitepaper, section 4 (checked October 18, 2026); Bitcoin Developer Guide, Proof of Work (checked October 18, 2026).
The work: keep trying
A miner builds a block candidate and its header. Mining hardware changes the nonce and hashes the header again and again. If a hash falls below the target, the miner has found proof of work and can send the block to the network. Miners can also change extra nonce data in the coinbase transaction to get fresh header data to try.
There is no clever shortcut hiding under the sofa. Each attempt is a new lottery ticket. Changing a past block means redoing its work and the work of later blocks built on it. Bitcoin whitepaper, section 4; Bitcoin Developer Guide, Mining (both checked October 18, 2026).
The target: the height of the bar
The target is the cutoff. A hash below it qualifies; a lower target makes qualifying hashes rarer. The Bitcoin Wiki's Difficulty page defines difficulty as a measure of how hard it is to find a hash below the target. Its Target page says the network adjusts the target every 2,016 blocks toward an average pace of one block per 10 minutes. Those are the adjustment interval and goal; no kitchen timer promises every block will arrive on schedule. Bitcoin Wiki, Difficulty; Bitcoin Wiki, Target (checked October 18, 2026).
Difficulty is a comparison, not a separate riddle. More difficulty means a tighter cutoff and fewer winning hashes per attempt. The target is stored in a compact form, so we are keeping our chalkboard drawing simple.
What the proof does not do
Finding a qualifying hash does not let a miner sneak any transaction into a block. Nodes check that transactions are valid and not already spent. Proof shows work was done; validation checks the rules. Think bouncer plus ticket stub, not “I solved a math problem, so the nachos are mine.” Bitcoin whitepaper, section 5; Bitcoin Developer Guide, Block Chain (checked October 18, 2026).
What we did not check
We did not inspect current network difficulty, miner hardware, energy use, or the chance that any particular miner will find a block. Those change over time or depend on details outside this explainer. The raffle picture describes the search, not a perfect simulation of mining.
Sources
- Bitcoin whitepaper, section 4: Proof-of-Work (checked October 18, 2026)
- Bitcoin Wiki: Difficulty (checked October 18, 2026)
- Bitcoin Wiki: Target (checked October 18, 2026)
- Bitcoin Developer Guide: Mining (checked October 18, 2026)
- Bitcoin Developer Guide: Block Chain (checked October 18, 2026)