Why an indicative calculation is only part of the assessment

An indicative calculation takes figures that have already been adjusted under the GloBE rules and works through the arithmetic: the substance-based income exclusion, the effective tax rate for the jurisdiction, the top-up percentage, excess profit, any credit for a domestic minimum top-up tax, and the resulting jurisdictional top-up tax.

That is genuinely useful. It shows which jurisdictions are near the minimum rate, how much of the profit is sheltered by substance, and how sensitive the result is to a change in one input. It is a planning and triage tool.

The arithmetic is only as good as the inputs, and the inputs are the hard part. GloBE income and adjusted covered taxes have to be prepared under the rules before the calculation starts, including the deferred tax treatment and the defined adjustments.

A calculation also assumes a settled group boundary: that the ultimate parent is correctly identified, that entity classifications are right, and that the jurisdiction being tested contains the entities it should. Change any of those and the number changes with it.

The transitional country-by-country reporting safe harbour, the domestic minimum top-up tax safe harbour and the other current safe harbours are conditions to be met and, in several cases, elections to be made. They are not produced by the calculation; they are tested against qualifying data, for a specific jurisdiction and period.

Two further points follow. A safe harbour is applied by the jurisdiction imposing the rule, which may not be the jurisdiction being tested. And an agreement reached at international level is not the same as a rule in force domestically, which has to be confirmed jurisdiction by jurisdiction.

Relief from top-up tax does not remove registration, notification, return or record-keeping obligations. A group can owe nothing in a jurisdiction and still be required to register there, file locally, or support a safe harbour claim with evidence.

The reporting side also has its own shape: a GloBE Information Return filed and exchanged in one place may relieve filing elsewhere, while local returns continue. Those arrangements are worth mapping early, because they determine who files what, and where.

A jurisdictional top-up tax figure does not say who pays it. That depends on the ordering of the domestic top-up tax, the Income Inclusion Rule and the Undertaxed Profits Rule, on the ownership structure above the entities concerned, and on the coordination rules that apply.

Used well, an indicative calculation tells you where to look and what to ask. The assessment is what turns that into a position: the right inputs, the applicable reliefs, the responsible entities and the filings each jurisdiction requires.