The allowance cannot reduce taxable salary below the applicable expertise threshold. If a full 30% allowance would do so, the tax-free amount is restricted to the difference between total wage including the allowance and the required taxable salary.
Example: with total wage of €50,000 and the standard 2026 threshold, a full €15,000 allowance is not possible. The maximum illustrated allowance is approximately €1,987, leaving taxable salary at €48,013.
Your employer can also agree a lower percentage. Payroll treatment can differ from this simplified annual model.