Ninety-Ninety Rule

What Does Ninety-Ninety Rule Mean?

The “ninety-ninety” rule states that the first 90 percent of code construction uses up 90 percent of development time, and that the remaining 10 percent of code construction accounts for another 90 percent. With a total adding up to 180 percent, this IT saying is clearly satirical.


It has sometimes been called the “rule of credibility” and often attributed to Tom Cargill of Bell Labs, or John Bentley’s articles in “Communications of the ACM.”

Techopedia Explains Ninety-Ninety Rule

The idea behind the “ninety-ninety” rule is that in the first 90 percent of a project, code construction takes place in a steady and linear way. The last 10 percent of construction is often where more challenges might present themselves, for instance, in debugging, fixing tougher sets of features, or putting the finishing touches on a project. There is the idea that the home stretch is where projects become really difficult, and start to suffer from time bloat. Another way to put this is that projects tend to be “resistant to ultimate signoff” when they are nearing completion.


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Margaret Rouse

Margaret Rouse is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical, business audience. Over the past twenty years her explanations have appeared on TechTarget websites and she's been cited as an authority in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine and Discovery Magazine.Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages. If you have a suggestion for a new definition or how to improve a technical explanation, please email Margaret or contact her…