There is no single rate; it varies with the strength of the file, the type of item and the conditions of the period. A realistic range can only be built together with an analysis of the litigation prospects, which we model before going to the table.
It also helps to put the expectation in the right place. The negotiating room lies mostly in the penalties and the late-payment interest; reduction in the tax principal itself is limited. And pre-assessment settlement usually offers more room than settlement after assessment, because you come to the table before a penalty has been issued at all. Which route suits your file is assessed item by item.
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