I seem to recall, long ago, being told that difficulty couldn't change more than a certain amount at each retarget, but I can't seem to find what that factor is (or even confirmation that such a factor exists) no matter how hard I google. Does such a factor exist and if so what is its value?

2 Answers 2


The difficulty never changes by more than a factor of 4 (except for in a special case that only applies on testnet).

The code that enforces this is here.


Well doesn't that figure, the moment I ask the question my google-fu kicks in.

This wiki article states:

A single retarget never changes the target by more than a factor of 4 either way to prevent large changes in difficulty.

  • Ah, gotta love moments like this! ;)
    – ThePiachu
    Jun 23, 2012 at 0:08
  • Yeah, I seriously think there's something about the act of phrasing a question for SE that activates some hidden bit of gray matter and creates superior search terms. It's not so annoying when it's an hour later, this one was mere seconds :P Jun 23, 2012 at 0:13
  • 1
    Well, it's still a good question and a good answer.
    – ThePiachu
    Jun 23, 2012 at 0:27
  • Interesting that the article would consider a change from the currently difficult of 1,726,567 to either 5,000,000 or 500,000 as not being a large change... I guess it's considering it from a logarithmic perspective? Jun 23, 2012 at 1:03

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