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  "id": "bitcoin-block-time-variance",
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  "collection": "bitcoin",
  "title": "Why Bitcoin blocks sometimes take an hour",
  "description": "Understand why Bitcoin blocks can arrive seconds or much longer apart even though the target interval is about ten minutes.",
  "aliases": [
    "bitcoin block taking an hour",
    "bitcoin block taking an hour explained"
  ],
  "dates": {
    "published": "2026-10-02",
    "modified": "2026-10-02",
    "verified": "2026-10-02T19:29:20.637Z",
    "dataAsOf": "2026-10-02"
  },
  "authorship": {
    "publisher": "Degrees of Satoshi editorial project",
    "process": "AI-assisted research and drafting with a separate automated source-verification pass; no external expert or named human review is implied."
  },
  "quickAnswer": {
    "text": "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.",
    "claimId": "bitcoin-block-time-variance-quick-answer",
    "sourceIds": [
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      "x425-btc-dev-block-chain",
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  "keyFacts": [
    {
      "label": "Target",
      "value": "About ten minutes per block on average",
      "sourceIds": [
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      ],
      "id": "target",
      "claimId": "bitcoin-block-time-variance-fact-target"
    },
    {
      "label": "Individual gap",
      "value": "Can be much shorter or longer",
      "sourceIds": [
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      "id": "individual-gap",
      "claimId": "bitcoin-block-time-variance-fact-individual-gap"
    },
    {
      "label": "Model condition",
      "value": "A fixed effective block-finding rate",
      "sourceIds": [
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      ],
      "id": "model-condition",
      "claimId": "bitcoin-block-time-variance-fact-model-condition"
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  ],
  "prerequisites": [
    "bitcoin-difficulty-adjustment",
    "bitcoin-confirmations"
  ],
  "sections": [
    {
      "id": "model",
      "heading": "A random search does not run on a timetable",
      "sourceIds": [
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        "x425-btc-dev-mining"
      ],
      "paragraphs": [
        "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."
      ]
    },
    {
      "id": "example",
      "heading": "A thirty-minute gap is unusual but possible",
      "sourceIds": [
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      ],
      "paragraphs": [
        "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."
      ]
    },
    {
      "id": "payments",
      "heading": "Block arrival and your transaction’s inclusion are separate",
      "sourceIds": [
        "x425-btc-dev-mining",
        "x425-btc-dev-payment-processing"
      ],
      "paragraphs": [
        "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."
      ]
    }
  ],
  "faq": [
    {
      "question": "After twenty minutes without a block, is one due in the next few seconds?",
      "answer": "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.",
      "sourceIds": [
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      ]
    },
    {
      "question": "Does one confirmation always take ten minutes?",
      "answer": "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.",
      "sourceIds": [
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        "x425-btc-dev-payment-processing"
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      "statement": "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.",
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      "sourceLocators": [
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          "locator": "Block Height And Forking; Transaction Data; Proof Of Work; Consensus Rule Changes"
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          "sourceId": "source-0e46aca4dbc5a030",
          "locator": "Sections 4, 6, 7, 10 and 11"
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      ],
      "scope": {
        "collection": "bitcoin",
        "dataAsOf": "2026-10-02",
        "blockHeight": null
      },
      "qualification": "Educational explanation. Product-specific behavior is scoped to the cited documentation, checked 2026-10-02.",
      "evidenceStatus": "documented",
      "verification": {
        "status": "verified",
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        "checkedAt": "2026-10-02T19:29:20.637Z",
        "reviewer": "Independent automated verification — Codex /root/verify_ethereum_100, separate from the Bitcoin drafting agent",
        "notes": [
          "Recomputedexp(-3)=4.98%andexp(-6)=0.248%under specified stable-rate windows and checked memoryless conditional waiting. The explanation does not confuse a fixed interval with a day’s maximum gap, or block arrival with transaction inclusion."
        ]
      }
    },
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      "id": "bitcoin-block-time-variance-fact-target",
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      "statement": "Target: About ten minutes per block on average",
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        {
          "sourceId": "source-190b9fe0eec933dc",
          "locator": "Block Height And Forking; Transaction Data; Proof Of Work; Consensus Rule Changes"
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      "scope": {
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        "notes": [
          "Recomputedexp(-3)=4.98%andexp(-6)=0.248%under specified stable-rate windows and checked memoryless conditional waiting. The explanation does not confuse a fixed interval with a day’s maximum gap, or block arrival with transaction inclusion."
        ]
      }
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        "notes": [
          "Recomputedexp(-3)=4.98%andexp(-6)=0.248%under specified stable-rate windows and checked memoryless conditional waiting. The explanation does not confuse a fixed interval with a day’s maximum gap, or block arrival with transaction inclusion."
        ]
      }
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          "locator": "Sections 4, 6, 7, 10 and 11"
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  ],
  "sources": [
    {
      "id": "x425-btc-know",
      "label": "Some things you need to know",
      "publisher": "Bitcoin.org",
      "url": "https://bitcoin.org/en/you-need-to-know",
      "locator": "Bitcoin payments are irreversible; Unconfirmed transactions aren't secure; You are your own bank; Bitcoin is not anonymous",
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      "locator": "Block Height And Forking; Transaction Data; Proof Of Work; Consensus Rule Changes",
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      "id": "x425-btc-whitepaper",
      "label": "Bitcoin: A Peer-to-Peer Electronic Cash System",
      "publisher": "Satoshi Nakamoto",
      "url": "https://bitcoin.org/bitcoin.pdf",
      "locator": "Sections 4, 6, 7, 10 and 11",
      "note": "Independent hash attempts, incentives, transaction collaboration limits and Poisson block-arrival approximation.",
      "version": "2008 paper",
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      "locator": "Mining; Solo Mining; Pool Mining; Block Prototypes",
      "note": "Hardware work, candidate blocks and pool shares; historical examples are not current equipment recommendations.",
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  "related": {
    "articles": [
      "bitcoin-difficulty-adjustment",
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      "can-bitcoin-be-frozen",
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  "revisionHistory": [
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      "kind": "published",
      "summary": "First publication after primary-source research and separate automated verification."
    }
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  "citation": "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/"
}