BA-08 · LESSON 03

Difficulty adjustment

Bitcoin retargets periodically to keep average block production near ten minutes despite changing hash rate.

Key terms in this lesson 2 definitions

Hash rate: The number of mining hash attempts performed per second.
Proof-of-work target: The maximum header-hash value accepted for a block; lowering it makes valid hashes harder to find.

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VISUAL MODEL

See the whole mechanism before going step by step

Use the diagrams to orient yourself. Then the guided explanation below teaches every part in depth.

4 explanatory views

CONCEPT-SPECIFIC MAP · difficulty adjustmentRetargeting changes the proof-of-work target after 2,016 blocksSelect any state to inspect its exact role.

RELATIONSHIP MAPOrdered mechanism flow

01
WINDOW2,016 blocks
The calculation uses timestamps spanning one retarget period.
02
EXPECTED1,209,600 seconds
Two weeks corresponds to an average of ten minutes per block.
03
ACTUAL1,209,600 seconds
A faster period implies more hash rate relative to the old target.
04
NEW TARGETOld target unchanged
A smaller target makes acceptable hashes rarer and difficulty higher.
05
NEXT BLOCKSame difficulty
Nodes derive and enforce the required target independently.

Rule shown: Bitcoin multiplies the old target by actual timespan divided by two weeks, bounded to one quarter through four times the target timespan.

STAGE 1 OF 5WINDOW: 2,016 blocks

The calculation uses timestamps spanning one retarget period.

Governing relationship: Bitcoin multiplies the old target by actual timespan divided by two weeks, bounded to one quarter through four times the target timespan. Complete path: 1. WINDOW, 2,016 blocks. The calculation uses timestamps spanning one retarget period. 2. EXPECTED, 1,209,600 seconds. Two weeks corresponds to an average of ten minutes per block. 3. ACTUAL, 1,209,600 seconds. A faster period implies more hash rate relative to the old target. 4. NEW TARGET, Old target unchanged. A smaller target makes acceptable hashes rarer and difficulty higher. 5. NEXT BLOCK, Same difficulty. Nodes derive and enforce the required target independently.

1. State transitionWhat exists, what changes, and what results

BEFORE

An adjustment period is mined in 7 days instead of the intended 14, with simplified timestamps and no clamp edge.

MECHANISM

The target normally remains constant within a 2,016-block interval, subject to network-specific exceptions.

AFTER

Difficulty responds after a period, so sudden hash-rate changes temporarily change block intervals.

Text equivalent: Starting from An adjustment period is mined in 7 days instead of the intended 14, with simplified timestamps and no clamp edge. The mechanism begins when The target normally remains constant within a 2,016-block interval, subject to network-specific exceptions. The resulting lesson is Difficulty responds after a period, so sudden hash-rate changes temporarily change block intervals.

2. Mechanism pathSelect a stage to inspect its job

STAGE 1 OF 5

Complete an adjustment period

The target normally remains constant within a 2,016-block interval, subject to network-specific exceptions.

Complete path: 1. Complete an adjustment period: The target normally remains constant within a 2,016-block interval, subject to network-specific exceptions. 2. Measure timestamp span: At the boundary, consensus uses defined block timestamps from the period to calculate how long mining appeared to take. 3. Clamp the ratio: The measured span is limited to between one-quarter and four times the target span, limiting one adjustment to a fourfold change. 4. Scale the target: If blocks were twice as fast, target is roughly halved, making mining twice as hard. If twice as slow, target roughly doubles. 5. Validate independently: Every node recomputes the permitted target from chain history and rejects a boundary block using a different target.

3. Rule and failure boundaryWhat accepts the result and where it can stop

ACCEPTED PATH

At the 2,016-block boundary, nodes multiply the prior target by actual divided by intended timespan after clamping that ratio to one quarter through four.

CHANGED CONDITION

A zero or noninteger timespan is outside the calculation, while a 100-day observation is capped rather than producing an unbounded target increase.

Important distinction: Difficulty changes after every slow or fast block to force the next block to take ten minutes. Mainnet retargets every 2,016 blocks. Individual block times remain highly variable even at the correct expected rate.

Text equivalent: The accepted path is enforced by At the 2,016-block boundary, nodes multiply the prior target by actual divided by intended timespan after clamping that ratio to one quarter through four. If the required condition changes, A zero or noninteger timespan is outside the calculation, while a 100-day observation is capped rather than producing an unbounded target increase.

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Learn the idea

Bitcoin adjusts proof-of-work difficulty every 2,016 blocks. Nodes compare the period's actual timestamp span with the two-week target span, clamp extreme adjustment, and derive a new target. The rule aims for a long-run average near ten minutes per block, not an exact schedule for each block.

GUIDED EXPLANATION1/5 ideas inspected

Complete an adjustment period

The target normally remains constant within a 2,016-block interval, subject to network-specific exceptions.

The worked example follows the explanation

Inspect every idea above to open it.

Important distinction“Difficulty changes after every slow or fast block to force the next block to take ten minutes.”

Mainnet retargets every 2,016 blocks. Individual block times remain highly variable even at the correct expected rate.

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