The new U.S. tax law could throw a monkey wrench into a method many analysts and investors use to gauge the strength of companies’ earnings.

A provision of the tax overhaul enacted in December assesses a one-time tax on companies’ accumulated earnings from outside the U.S. But while the tax is typically charged to companies’ 2017 earnings, firms have the option of stretching the actual tax payment over the next eight years, interest free.

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