# Why Bitcoin blocks sometimes take an hour

Bitcoin’s ten-minute target is an average, not a schedule for individual blocks. Miners repeatedly test candidate hashes, and successful attempts arrive irregularly. Under a stable-rate model, the waiting time is approximately exponential: a long gap is possible, and an unsuccessful wait does not make the next block due. Actual conditions can change when hash rate changes or difficulty adjusts.

Evidence: [Some things you need to know](https://bitcoin.org/en/you-need-to-know); [Block Chain](https://developer.bitcoin.org/devguide/block_chain.html); [Bitcoin: A Peer-to-Peer Electronic Cash System](https://bitcoin.org/bitcoin.pdf)

Canonical: https://degreesofsatoshi.com/encyclopedia/bitcoin-block-time-variance/
Published: 2026-10-02
Substantively modified: 2026-10-02
Independently verified by an automated reviewer: 2026-10-02T19:29:20.637Z
Data current through: 2026-10-02

AI-assisted research and drafting with a separate automated source-verification pass; no external expert or named human review is implied.

## Key facts

- **Target:** About ten minutes per block on average ([Block Chain](https://developer.bitcoin.org/devguide/block_chain.html))
- **Individual gap:** Can be much shorter or longer ([Some things you need to know](https://bitcoin.org/en/you-need-to-know))
- **Model condition:** A fixed effective block-finding rate ([Bitcoin: A Peer-to-Peer Electronic Cash System](https://bitcoin.org/bitcoin.pdf))

## A random search does not run on a timetable

Each candidate hash either meets the target or does not. Under the idealized independent-attempt model, there is no accumulated progress meter that forces a success when ten minutes have elapsed.

Difficulty controls the success threshold. Changing effective hash rate changes the rate of successful attempts until difficulty responds; the simple ten-minute model is an assumption for explanation, not a live measurement.

Evidence: [Bitcoin: A Peer-to-Peer Electronic Cash System](https://bitcoin.org/bitcoin.pdf); [Mining](https://developer.bitcoin.org/devguide/mining.html)

## A thirty-minute gap is unusual but possible

Assuming a constant average interval of ten minutes, the probability of no block during a specified 30-minute period is exp(−30/10), about 4.98%. For a specified 60-minute period it is exp(−6), about 0.248%. These are model calculations, not forecasts for a particular day.

The probability refers to each stated observation window. It is not the probability that a whole day contains no long gap, which asks a different question.

Evidence: [Bitcoin: A Peer-to-Peer Electronic Cash System](https://bitcoin.org/bitcoin.pdf); [Some things you need to know](https://bitcoin.org/en/you-need-to-know)

## Block arrival and your transaction’s inclusion are separate

Even when a block arrives, it may not contain a particular transaction. Miners select transactions and must respect validity and dependency requirements. Fees and local policy can affect which pending transactions they choose.

A wallet’s confirmation estimate therefore combines uncertainty about block timing with uncertainty about inclusion. A long wait does not alone prove a lost payment or a stopped network.

Evidence: [Mining](https://developer.bitcoin.org/devguide/mining.html); [Payment Processing](https://developer.bitcoin.org/devguide/payment_processing.html)

## Questions

### After twenty minutes without a block, is one due in the next few seconds?

Not under the constant-rate independent-search model. The future waiting time does not shorten merely because the previous interval was unsuccessful. Actual changes in hash rate can change the model’s rate.

Evidence: [Bitcoin: A Peer-to-Peer Electronic Cash System](https://bitcoin.org/bitcoin.pdf)

### Does one confirmation always take ten minutes?

No. Ten minutes is an average target for blocks, and a transaction is not guaranteed inclusion in the next one. Actual confirmation time can be much shorter or longer.

Evidence: [Some things you need to know](https://bitcoin.org/en/you-need-to-know); [Payment Processing](https://developer.bitcoin.org/devguide/payment_processing.html)

## Claims and scope

### bitcoin-block-time-variance-quick-answer

Bitcoin’s ten-minute target is an average, not a schedule for individual blocks. Miners repeatedly test candidate hashes, and successful attempts arrive irregularly. Under a stable-rate model, the waiting time is approximately exponential: a long gap is possible, and an unsuccessful wait does not make the next block due. Actual conditions can change when hash rate changes or difficulty adjusts.

Educational explanation. Product-specific behavior is scoped to the cited documentation, checked 2026-10-02.

Scope: {"collection":"bitcoin","dataAsOf":"2026-10-02","blockHeight":null}

### bitcoin-block-time-variance-fact-target

Target: About ten minutes per block on average

Scope: {"collection":"bitcoin","dataAsOf":"2026-10-02","blockHeight":null}

### bitcoin-block-time-variance-fact-individual-gap

Individual gap: Can be much shorter or longer

Scope: {"collection":"bitcoin","dataAsOf":"2026-10-02","blockHeight":null}

### bitcoin-block-time-variance-fact-model-condition

Model condition: A fixed effective block-finding rate

Scope: {"collection":"bitcoin","dataAsOf":"2026-10-02","blockHeight":null}

## Sources

- [Some things you need to know](https://bitcoin.org/en/you-need-to-know) — Bitcoin.org. Payment reversibility, confirmation risk and visible transaction records. Locator: Bitcoin payments are irreversible; Unconfirmed transactions aren't secure; You are your own bank; Bitcoin is not anonymous. Retrieved: 2026-10-02T18:53:53.609Z.
- [Block Chain](https://developer.bitcoin.org/devguide/block_chain.html) — Bitcoin developer documentation. Chain validation, block timing, proof of work and accepted-chain context. Locator: Block Height And Forking; Transaction Data; Proof Of Work; Consensus Rule Changes. Retrieved: 2026-10-02T18:53:53.957Z.
- [Bitcoin: A Peer-to-Peer Electronic Cash System](https://bitcoin.org/bitcoin.pdf) — Satoshi Nakamoto. Independent hash attempts, incentives, transaction collaboration limits and Poisson block-arrival approximation. Locator: Sections 4, 6, 7, 10 and 11. Retrieved: 2026-10-02T18:53:58.187Z.
- [Mining](https://developer.bitcoin.org/devguide/mining.html) — Bitcoin developer documentation. Hardware work, candidate blocks and pool shares; historical examples are not current equipment recommendations. Locator: Mining; Solo Mining; Pool Mining; Block Prototypes. Retrieved: 2026-10-02T18:53:53.955Z.
- [Payment Processing](https://developer.bitcoin.org/devguide/payment_processing.html) — Bitcoin developer documentation. Payment request interpretation, confirmation checks and refund destination risks; historical protocol sections are dated. Locator: Requesting Payments; Verifying Payment; Issuing Refunds. Retrieved: 2026-10-02T18:53:53.958Z.

## Revision history

- 2026-10-02: First publication after primary-source research and separate automated verification.

## Cite this entry

Degrees of Satoshi editorial project. “Why Bitcoin blocks sometimes take an hour.” Published 2026-10-02; updated 2026-10-02. https://degreesofsatoshi.com/encyclopedia/bitcoin-block-time-variance/