What the combined corporate income tax rate is
The combined corporate income tax rate adds sub-central company taxes to the central statutory rate. It is the better single number for federal countries such as the United States, Canada, Germany or Switzerland, where states, provinces or cantons levy their own corporate taxes on top of the national rate. The sub-central share varies by location, so the combined figure is not a single rate that any one company necessarily pays.
Where the OECD source does not publish a combined figure, the country is absent from this leaderboard. The central-only statutory rate is on the corporate income tax page.
Combined rates move when either layer moves: a change in the national rate or in the average sub-central rate shifts the figure, and the OECD recalculates the sub-central share as tax laws change. Reading the combined series against the central-only page is the clearest picture of how much of a country's company tax is raised below the national level — for the United States, for example, a 21% federal rate sits under a combined measure that reflects state taxes on top.