tax-free ratio; tax-free percentage
Used in economic, accounting, or tax contexts to refer to the proportion of income, goods, or transactions that are exempt from taxation.
The tax-free ratio for this product is 8%.
At duty-free shops, the tax-free percentage may vary depending on the purchase amount.
税率 (tax rate) is the percentage at which something is taxed, whereas 免税率 is the percentage that is exempt from tax.
Compound of 免税 (tax exemption) + 率 (rate, ratio). The derivation is straightforward from its components.