Over the course of the last year, it has become clear that Democratic lawmakers want to change U.S. tax rules for large companies. However, as proposals have been debated in recent months, there are have been clear divides between U.S. proposals and the global minimum tax rules.

Before getting too far into the weeds, it is worth noting that I am no fan of minimum taxes and it would be nice if Congress would change the underlying tax code to limit credits or deductions they think are too generous rather than complicate things further with new definitions of income and opaque rules. Simplicity matters.

The Inflation Reduction Act (IRA) to be considered by Congress in the coming days includes an alternative minimum tax on companies that at first glance may seem like it was inspired by (or at least might be like) the global minimum tax. Both taxes are aimed at large companies, use financial accounting rules for the tax base, and apply a 15 percent rate. That is where the similarities end.

However, those similarities could lead some to suggest the U.S. is adopting measures in line with the global minimum tax, but that is not entirely accurate.

As shown in the following table, there are multiple differences between the policies. In some areas, the policies take directly opposite approaches. In short, the Inflation Reduction Act policy is kind to tax credits and stingy toward write-offs for capital investments while the global minimum tax is stingy toward tax credits while being kind to write-offs for capital investments.

If the Inflation Reduction Act gets adopted in the United States and the global minimum tax is adopted elsewhere, the differences between the policies could create stinginess toward both write-offs for capital investments and tax credits for the largest companies.

The global minimum tax is part of an agreement among more than 130 jurisdictions that was reached in 2021. In December 2021 model rules were released that described how the rules were meant to work.

The rules have three main layers. The first applies to purely domestic income (Qualified Domestic Minimum Top-up Tax), the second applies to foreign income in a company’s subsidiaries (Income Inclusion Rule), and the third applies to the income of foreign entities that are not subject to the prior two rules (the Undertaxed Profits Rule (UTPR)).

The global minimum tax applies to companies with more than €750 million (US $769 million) in revenues, and it levies a 15 percent minimum rate on a company’s financial accounting income after several adjustments including adjustments for taxes that have already been paid.

The corporate alternative minimum tax in the Inflation Reduction Act first came to light as part of a presidential campaign proposal from Sen. Elizabeth Warren (D-MA). It was also included in the Build Back Better Act which passed the House of Representatives in the fall of 2021. All of this happened before the global minimum tax model rules were released. The current proposal in the Inflation Reduction Act applies to companies with more than $1 billion in financial profits and levies a 15 percent rate on adjusted financial accounting income.

The key differences between the policies lie in the adjustments to financial accounting income. As a reminder, financial income is what companies report to their shareholders and is calculated using accounting rules established by those in charge of accounting standards (the Financial Accounting Standards Board in Norwalk, CT). Taxable income is calculated using different rules (as defined in Title 26 of the U.S. Code).

If pure financial accounting income were adopted, the policy would erode tax credits and deductions for capital investments that can push tax rates below the 15 percent minimum in years when companies are heavily investing in things like research and development or building factories and purchasing lots of equipment.

The Inflation Reduction Act corporate alternative minimum tax provides an exemption for tax credits. This means that even if a tax credit pushes a company’s tax rate on their financial statement below 15 percent, the credit would not get clawed back by the minimum tax. The global minimum tax, however, only provides an exemption for certain tax credits including those that are payable to businesses (also known as refundable tax credits). If a company benefits from the U.S. research and development credit, it would get clawed back, though.

The Inflation Reduction Act provides no exemptions for deductions for capital investments. This is a key contributor to the fact that nearly half of the tax increase would fall on manufacturers according to the Joint Committee on Taxation. The global minimum tax is more generous to capital investment in two ways. First, deductions for capital investment are measured at a 15 percent tax rate rather than being fully clawed back. Also, the global minimum tax has a carveout for tangible assets that reduces the amount of additional tax a company might have to pay even if its tax rate is below 15 percent.

The global minimum tax has an additional carveout for payroll costs which is not reflected in the Inflation Reduction Act corporate alternative minimum tax.

The mismatches between the policies mean that companies could end up facing both taxes. If a foreign jurisdiction that has adopted the global minimum tax rules is looking to tax a U.S. company that benefits from tax credits that are protected by the Inflation Reduction Act, then additional tax could be owed to that foreign jurisdiction. In that case the tax credits and deductions for capital investment could be caught by the two separate rules.

In other words, the Inflation Reduction Act does not reflect the rules of the global minimum tax, but rather represents an additional layer of tax on large companies. Put these two layers of tax together, in addition to the regular corporate tax, and we would now have three layers of complex, opaque tax rules for U.S. companies to deal with, each distorting business investment decisions in somewhat different ways and contributing to a higher overall tax burden on U.S. business investment.