The transitional CbCR safe harbour deems top-up tax to be zero in a jurisdiction where any one of three tests is met. The arithmetic is not hard. Knowing which constants apply to which year, and which ten things quietly disqualify you regardless, is the part that costs money. This does both, and shows its working.
This is a directional test. It tells you which tests your figures clear and by how much. It does not tell you that you are safe, it is not a filing position, and it is not advice. Take it to your adviser as a starting point rather than as a conclusion — the purpose is to make that conversation shorter and better informed, not to replace it.
Every figure you type stays in this browser tab. Nothing is transmitted, nothing is stored, and I never see any of it. Close the tab and it is gone.
The transition rate and the substance percentages both depend on the year the fiscal year begins, not the year it ends.
One block per jurisdiction. Figures in euro — the thresholds are euro-denominated and are rebased annually using the average ECB rate for December of the previous fiscal year. Leave a field blank where you do not have it; the tool will say which tests it cannot run.
Each of these can stop the safe harbour applying whatever the arithmetic above says. A tool that silently assumes none of them bite is worse than no tool, so this one asks.
These change the figures you type in. They are listed because getting them wrong is the most common way a correct-looking calculation produces a wrong answer.
Two grades, and the tool marks which applies to each number it uses. OECD means it was read from the OECD's own published text. Statute means the OECD text could not be retrieved and the figure rests on an enacting national statute instead. Nothing here was reconstructed from memory or taken from an advisory firm's summary of the rules.
The OECD Side-by-Side Package of 5 January 2026 extended the transition period by one year. Its paragraph 9 confirms the extension, but Section 3, which carries the amended wording, sits behind a path that blocks automated retrieval. The two dates used here come from HMRC draft legislation of 13 July 2026, which substitutes them explicitly. The 2027 transition rate rests on UK Schedule 16 paragraph 8(1)(c) being open-ended rather than on OECD text.
If you hold the OECD package and the wording differs from this, tell me and I will correct it the same week.
If this has shown you jurisdictions that clear a test, the next question is what you still have to file in each of them — because the safe harbour deems the tax to be zero, not the obligation to be gone. The scoping tool answers that part.