《去九法》是种验算加、减、乘运算的方法。

去九法的应用要追溯至萨珊王朝时代。当时伊斯兰文化贸易兴盛，应商业的需求，就产生了去九法，以验算交易中运算。

Casting out nines is a sanity test to ensure that hand computations of sums, differences, products, and quotients of integers are correct. By looking at the digital roots of the inputs and outputs, the casting-out-nines method can help one check arithmetic calculations. The method is so simple that most schoolchildren can apply it without understanding its mathematical underpinnings.