Benefit-in-kind tax has one moving part once you know the benefit's cash equivalent: multiply it by YOUR income-tax rate. A £5,000 cash equivalent on top of a £40,000 salary adds £1,000.00 of tax across 2026/27; the same benefit on £55,000 adds £2,000.00, because those pounds fall in the 40% band. Employee National Insurance is not charged on benefits: that is the one kindness in the system.
Step one: the cash equivalent
Every benefit type has a valuation rule set by HMRC: a company car uses list price × an emissions-based percentage, private medical insurance uses the premium the employer pays, a loan over £10,000 uses the official rate of interest on the balance. The employer reports the figure on your P11D or payrolls it monthly; you do not calculate it, you read it. This site quotes none of the per-benefit percentage tables because they change by year and benefit class: the GOV.UK page below is the authoritative table, and the number you need from it is a single cash equivalent.
Step two: your rate, not a special one
The cash equivalent is added to your taxable income and taxed in whatever band it lands in. On £40,000, a £5,000 benefit sits wholly in the basic band: £1,000.00. On £55,000 it sits in the higher band: £2,000.00, so the identical benefit costs twice as much. Straddle the £50,270 line and the benefit itself pushes some pounds into 40%: run your salary through the calculator first to see where your marginal rate sits, then price the benefit at that rate.
How the tax is actually collected
Either the employer payrolls the benefit (the cash equivalent ÷ 12 joins each payslip's taxable pay and the tax flows through PAYE), or HMRC adjusts your tax code down by the cash equivalent, collecting the same amount by shrinking your tax-free pay. A code like 757L instead of 1257L usually means £5,000 of benefits are being collected this way. Same tax either route; the payroll route just keeps the code clean and the P11D away.
Questions people ask about bik tax calculator
Do I pay National Insurance on a benefit in kind?
Employees do not: the employer pays Class 1A NI on it instead. Your cost is income tax on the cash equivalent, full stop.
Is salary sacrifice for a benefit still worth it?
For most benefits the sacrificed salary is taxed as if you still had it, killing the saving: the main exceptions are pensions, cycle-to-work and ultra-low-emission cars. Price it as: tax on the benefit versus tax and NI on the salary given up.
Why did a benefit change my tax code?
HMRC collects the benefit's tax by reducing your tax-free allowance. When the benefit ends, tell HMRC: the code does not fix itself mid-year.