What is mining difficulty? Bitcoin difficulty explained

Mining difficulty is a measure of how hard it is to find a valid new block on a proof of work blockchain such as Bitcoin. The network adjusts it automatically: when more miners join and blocks come too fast, difficulty increases; when miners leave and blocks slow down, difficulty decreases. On Bitcoin this happens every 2,016 blocks, so that new blocks keep arriving about every 10 minutes, whatever the total computing power.

What is mining difficulty?

Mining difficulty is a number that tells miners how much work it takes, on average, to mine a block. On the Bitcoin network, miners compete to find a block hash below a certain target value. The lower the target, the fewer valid hashes exist, and the more guesses every miner needs. Difficulty is simply that target expressed as a readable number: how many times harder it is now than at the minimum difficulty when Bitcoin started.

The higher the difficulty, the more hashes the whole network has to compute to find the next block. Bitcoin difficulty now runs into the trillions, which reflects the huge amount of specialised hardware mining it.

How mining difficulty works

Mining difficulty works through a guessing game that every miner plays for every new block.

1. Build a block header. A miner collects waiting transactions and creates a block header that includes the previous block’s hash, a timestamp and the current target.
2. Hash it. The miner runs the header through the SHA-256 hash function and gets a long number.
3. Compare with the target. If the block hash is below the current target, often described as starting with enough leading zeros, the block is valid. If not, the miner changes a small number in the header, called the nonce, and tries again.
4. Win the block. The first miner to find a valid block hash broadcasts it. Other miners verify transactions and the hash in an instant, and start on the next block.
5. Collect the reward. The winner receives the mining rewards: newly created bitcoin plus transaction fees.

Because each guess is random, nobody can find a valid hash faster except by making more guesses. That is why more computing power, or hashing power, gives a miner a bigger chance to mine a block. Read more under mining and proof of work.

The Bitcoin difficulty adjustment

The Bitcoin difficulty adjustment is the rule that keeps the block time close to 10 minutes. Every 2,016 blocks, a period known as a difficulty epoch, each node compares the actual time those blocks took with the expected time of two weeks (2,016 × 10 minutes = 14 days). Then it sets the new difficulty for the next epoch.

• If blocks were mined faster than expected, because more miners joined, the next difficulty goes up.
• If blocks were mined slower, because miners left, the difficulty change goes down.
• Each adjustment is capped at a factor of four in either direction.

Between adjustments, all miners work with the same difficulty. The network hash rate can rise or fall in the meantime, so blocks arrive faster or slower than 10 minutes until the next retarget.

A worked example

Say the last 2,016 blocks took 12 days instead of 14, because more miners came online. The network raises the difficulty by 14 ÷ 12 = 1.167, an increase of about 16.7%. If those blocks had taken 16 days, the difficulty would fall to 14 ÷ 16 = 0.875 of its old level, a drop of 12.5%.

Real events show the mechanism working. When China banned crypto mining in 2021, a large share of the network hash rate went offline, and Bitcoin recorded its biggest downward difficulty adjustment. Blocks sped back up to about 10 minutes once the difficulty dropped.

Difficulty, hash rate and the halving

Difficulty follows the hash rate, not the other way round. With a constant hashrate, difficulty stays roughly flat; when more miners join, it climbs after a delay. Websites show this as a bitcoin difficulty chart, and some offer a bitcoin difficulty estimator that predicts the next difficulty from the blocks mined so far.

Difficulty also protects Bitcoin’s coin issuance schedule. Every 210,000 blocks, about every four years, the reward per block is cut in half; since April 2024 it is 3.125 BTC. Because difficulty keeps blocks at regular intervals, halvings happen roughly on schedule and new bitcoin can’t be mined faster just because more machines join.

Network difficulty vs pool difficulty

Most miners join a mining pool, because finding a block alone could take years. The pool sets its own, much lower “share” difficulty to measure how much work each member contributes, while the network difficulty still decides when a real block is found. When the pool wins a block, it splits the reward among members by their shares.

Where to find the current Bitcoin difficulty

Block explorers and mining websites publish the current difficulty, a chart of its history and an estimate of the next retarget. The current BTC difficulty is also built into every block, so any node can check it.

Why mining difficulty matters to you

Mining difficulty matters to you as an investor mainly because it shows how much security protects the network. A higher difficulty means an attacker would need more hardware and energy to rewrite blocks, which makes the Bitcoin network harder to attack. It is not a price signal: difficulty reacts to miners’ decisions, often weeks after the price moves.

If you are thinking about mining yourself, difficulty is the reason it rarely pays at home in Europe:

• Your share shrinks as others join. The same machine earns less when difficulty increases.
• Electricity is the main cost. Specialised machines use a lot of power, and EU household prices are relatively high. Use a bitcoin mining calculator with your own electricity price and the current difficulty before you buy anything.
• Cloud mining is a common scam. Offers to “rent” mining power for a fixed daily return are often fraudulent, and regulators have repeatedly warned about them.
• Taxes apply. Mining rewards usually count as taxable income in EU countries.

Under MiCA, licensed crypto platforms must publish information on the environmental impact of each coin’s consensus mechanism, and proof of work mining at a high difficulty is the most energy-intensive kind.

Difficulty on other blockchains

Other proof of work coins use the same principle but adjust differently. Some retarget after every block instead of every 2,016 blocks, which reacts faster when many miners switch between coins. Proof of stake networks, such as Ethereum since 2022, don’t use mining difficulty at all, because validators are chosen by stake rather than by computing power.

The bottom line

Mining difficulty is Bitcoin’s built-in thermostat. It rises when miners pile in and falls when they leave, so blocks keep coming about every 10 minutes and new coins are issued on schedule. For investors, it is a gauge of network security, not a reason to buy or sell.

Related terms

• Mining
• Proof of work
• Hash Rate
• Halving
• Bitcoin