Ninety Ten Rule

The first ninety percent of the task takes ninety percent of the time, and the last ten percent takes the other ninety percent.

Incidentally, the first time this page was created, the sentence read The first ninety percent of the task takes ninety percent of the time, and the last ten percent takes the other ten percent. . . . I made a comment, waited, then refactored the quote. . . I am sure getting the bugs out took as long as it did to create the page

No, the original version is right. You plan your implementation, you start, everything is on track, you get 90% done taking 90% of your available time to do it, as planned. Then the remaining 10% takes just as much time again, if not more. It's a case of HaHaOnlySerious.

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See the EightyTwentyRule. Also see the TwentyEightyRule.

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Other contexts:

• SturgeonsLaw is that ninety percent of anything is crap. Software is not immune.
• 90% of the code is written by 10% of the programmers.