# Difficulty adjustment

Every 2,016 blocks, about two weeks, Bitcoin resets mining difficulty so blocks average 10 minutes again. Learn the formula and the limits.

Canonical page: https://mybitcoinexplorer.com/learn/difficulty-adjustment
Topic: Mining
Published: 2026-10-29
Updated: 2026-10-30


## Keeping time
If more miners join, blocks would come faster. If miners leave, slower. To keep the average at 10 minutes, Bitcoin recalculates difficulty every **2,016 blocks**, about two weeks.

> Diagram: Too fast? Difficulty goes up. Too slow? It goes down. — 

## The formula
~~~
new target = old target × (actual time for 2,016 blocks ÷ 20,160 minutes)
~~~

- Took 12 days instead of 14? Target shrinks by 12/14: about 17% harder.
- Took 16 days? Target grows by 16/14: about 12.5% easier.
- A single adjustment can't change difficulty by more than a factor of 4 either way.

## Why it matters
- **Predictable supply:** the [halving](https://mybitcoinexplorer.com/learn/bitcoin-halving) stays roughly every four years.
- **Self-correcting:** if a large part of hash power suddenly disappears, blocks slow down for at most one period, then difficulty drops.

> A quirk: the original code measures the time across 2,015 intervals, not 2,016. It has no practical effect today, and fixing it would need a consensus change.


## When is the next adjustment?
Take the current height, divide by 2,016 and round up to the next whole number: that multiple of 2,016 is the next adjustment height. For example, after block 973,000 the next is 973,728 (2,016 × 483).

## Famous adjustments
In mid-2021, after a large share of mining shut down in China, difficulty fell by about 28% in a single adjustment, one of the biggest drops ever, and block times recovered within weeks.


## Key takeaways

- Difficulty adjusts every 2,016 blocks (about two weeks).
- It scales with how long the last 2,016 blocks actually took.
- Each adjustment is capped at 4× in either direction.

## Common questions

### When is the next difficulty adjustment?

At the next block height that is a multiple of 2,016.

### Can difficulty go down?

Yes, whenever blocks came slower than 10 minutes on average in the previous period.

### How often does Bitcoin difficulty change?

Every 2,016 blocks, roughly every two weeks.

### What happens if many miners leave at once?

Blocks slow down until the next adjustment, which then lowers difficulty by up to a factor of 4.

## Related lessons

- [Target and difficulty](https://mybitcoinexplorer.com/learn/target-and-difficulty)
- [Hashrate](https://mybitcoinexplorer.com/learn/hashrate)
- [Block timestamps](https://mybitcoinexplorer.com/learn/block-timestamps)
- [The Bitcoin halving](https://mybitcoinexplorer.com/learn/bitcoin-halving)