Cumulative error is the error that occurs in an equation or estimation over time. It often starts with a small error in measurement or estimation which becomes much larger over time due to its constant repetition. Finding the cumulative error requires finding the error of the original equation and multiplying that error by the number of times the error has been repeated. This formula requires very basic arithmetic with or without a calculator.

Find the original error of your equation and subtract it from the actual result of your equation. For example, if you calculated your car payments to be $300 and they ended up being 350, subtract $350 from $300 to get -$50.

Remove the negative sign if your result is negative. For example, remove the negative sign from “-$50” to end up with “$50.”

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Calculate how many times the error has been made and multiply that by the original error to find your cumulative error. For example, if you made your car payment for 12 months before catching the error, calculate $50 by 12 to get $600.

Find the percentage error by dividing your cumulative error by the correct total. For example, you calculated your yearly car payments to be $300 multiplied by 12, which is $3,600. However, it is actually $350 multiplied by 12, which is $4,200. Divide your cumulative error of $600 by $4,200 to get 0.14.

Multiple the result by 100 to get the percentage. For example, you would multiple 0.14 by 100 to get 14 percent. Your cumulative error is $600 and your cumulative error percentage is 14 percent.