noun
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.
この商品の免税率は8%です。
The tax-free ratio for this product is 8%.
免税店では、購入金額に応じて免税率が変わることがあります。
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.