<p>There is an adjustment for the testnet when a block takes 20 minutes or longer to mine, it will adjust the difficulty down to 1. This was caused presumably because of the difference between blocktimes of <code>1356765</code> and <code>1356766</code> because block <code>1356767</code> was reset to 1.</p>

<p>Every 2016 blocks, the difficulty is adjusted, but it can only be increased by a factor of 4 each time.</p>

<p><code>pow.cpp</code> as of version 0.16.2</p>

<pre><code>// Special difficulty rule for testnet:
// If the new block's timestamp is more than 2* 10 minutes
// then allow mining of a min-difficulty block.
if (pblock-&gt;GetBlockTime() &gt; pindexLast-&gt;GetBlockTime() + params.nPowTargetSpacing*2)
    return nProofOfWorkLimit;
</code></pre>

CC BY-SA 4.0
2018-08-03T21:58:38.393Z
2018-08-04T03:03:27.933Z
2018-08-04T03:03:27.933Z
JBaczuk
<p>Bitcoin's difficulty adjusts only every 2016 blocks (though the calculation is done on the previous 2015 blocks, due to an off-by-one error), and there is a maximum limit to the degree of the adjustment. This means that when the hash rate spikes—as it does when someone points a whole rig to the testnet as @amaclin stated—it can take a while until the difficulty adjusts to the point where the block interval reaches 10 minutes again.</p>

CC BY-SA 4.0
2018-08-03T19:44:56.080Z
2018-08-31T19:56:20.030Z
2018-08-31T19:56:20.030Z
Gendarme
<blockquote>
  <p>why?</p>
</blockquote>

<p>Because someone set his mining software to testnet. Sorry, this answer is useless, but there is no better answer for this question :) I doubt that the owner of hash power would show his reasons. I do not want to speculate about testing new mining hardware by developers.</p>

CC BY-SA 4.0
2018-08-03T18:59:58.177Z
2018-08-03T18:59:58.177Z
amaclin
<p>The bitcoin test network is mining about 50 blocks every minute for the last several hours. What is going on?</p>

<p>You can see here: <a href="https://www.blocktrail.com/tBTC" rel="nofollow noreferrer">https://www.blocktrail.com/tBTC</a></p>

<bitcoin-core><bitcoind><testnet>
bitcoin testnet is mining about 50 blocks per minute right now - why?
sizzlecookie
# bitcoin testnet is mining about 50 blocks per minute right now - why?

(Asked by: username_0 on 2018-08-03)

The bitcoin test network is mining about 50 blocks every minute for the last several hours. What is going on?

You can see here: <https://www.blocktrail.com/tBTC>

**Tags:** bitcoin-core, bitcoind, testnet


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## 3 answers

### Answer by username_3 on 2018-08-03. Score: 3 | Accepted answer

> why?

Because someone set his mining software to testnet. Sorry, this answer is useless, but there is no better answer for this question :) I doubt that the owner of hash power would show his reasons. I do not want to speculate about testing new mining hardware by developers.


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### Answer by username_1 on 2018-08-03. Score: 6

There is an adjustment for the testnet when a block takes 20 minutes or longer to mine, it will adjust the difficulty down to 1. This was caused presumably because of the difference between blocktimes of `1356765` and `1356766` because block `1356767` was reset to 1.

Every 2016 blocks, the difficulty is adjusted, but it can only be increased by a factor of 4 each time.

`pow.cpp` as of version 0.16.2

```
// Special difficulty rule for testnet:
// If the new block's timestamp is more than 2* 10 minutes
// then allow mining of a min-difficulty block.
if (pblock->GetBlockTime() > pindexLast->GetBlockTime() + params.nPowTargetSpacing*2)
    return nProofOfWorkLimit;

```


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### Answer by username_2 on 2018-08-03. Score: 0

Bitcoin's difficulty adjusts only every 2016 blocks (though the calculation is done on the previous 2015 blocks, due to an off-by-one error), and there is a maximum limit to the degree of the adjustment. This means that when the hash rate spikes—as it does when someone points a whole rig to the testnet as @username_3 stated—it can take a while until the difficulty adjusts to the point where the block interval reaches 10 minutes again.


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