Say a company had $100 in income. At today’s 21 percent corporate federal income tax rate, its federal income tax expense would be $21. Under the disclosure rule, that company would have to divulge any particular tax expenses that exceeded $1.05 (5 percent of $21).

For companies that were big users of tax havens before the passage of the 2017 law, the GILTI tax was expected to be a significant new expense — and one that would presumably have to be individually disclosed. A small number of companies, including Netflix and Bristol Myers, the pharmaceutical giant, did so in their 2018 annual reports.

But many of the companies that were most likely to face a large bill from the new tax — like Apple, Google, Microsoft and Facebook — have not disclosed how much the GILTI tax took out of their earnings.

Understanding the GILTI silence

The lack of disclosure may be masking the financial impact of how the Trump administration is writing rules governing how the 2017 tax package is enacted. Under pressure from corporate lobbyists, the Treasury Department has allowed multinational companies to partly or completely avoid taxes on certain overseas income.

Tax experts told The New York Times that the impact of those weakened rules, while hard to measure precisely, is likely to exceed $100 billion.

The companies’ silence about what they actually are paying under the GILTI makes it hard to quantify the true costs of the Treasury’s rules.

It’s possible that some companies did not reveal how much the GILTI tax was costing them because, after accounting for tax credits and other factors, the amount fell below the 5 percent threshold. Microsoft said that was the case with its GILTI tax in its 2019 fiscal year.