In corporate finance, net operating profit after tax (NOPAT) is a company's after-tax operating profit for all investors, including shareholders and debt holders. NOPAT is used by analysts and investors as a precise and accurate measurement of profitability to compare a company's financial results across its history and against competitors. 
When calculating NOPAT, one removes Interest Expense and the effects of other non-operating activities (non-recurring gains and losses) from Net Income to arrive at a value that approximates the value of a firm's annual earnings. NOPAT is precisely calculated as:
NOPAT = (Net Income - after-tax Non-operating Gains + after-tax Non-operating Losses + after-tax Interest Expense)
NOPAT doesn’t include one-time losses and other non-recurring charges because they don’t represent the true, on-going profitability of the business.  For example, a company may incur acquisition costs that would not be expected to occur in the future. These costs would negatively effect current year earnings, but do not accurately portray the operations of the firm. These costs should be excluded when performing any type of analysis to determine the operating and financial efficiency of a firm or to compare performance against other firms.
For a rough calculation, NOPAT approximates earnings before interest after taxes (EBIAT).
The rough calculation for NOPAT is:
|- Non-operating Gains after taxes||30|
|+ Non-operating Losses after taxes||40|
|+ Interest expense after taxes||50|
- G. Benett Stewart III (1991). The Quest for Value. HarperCollins.
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- "Net Operating Profit After-Tax". NewConstructs.com. Retrieved 7 May 2015.