Estimate your annual and monthly company car tax
How company car income tax is calculated
Company car tax is typically based on the benefit-in-kind (BIK) value of the vehicle. In practical terms, tax authorities treat private use of a company vehicle as a taxable benefit. The higher the car’s list value and BIK percentage, the more taxable benefit you report.
This calculator helps you estimate your likely annual and monthly tax cost from three core items:
- P11D value (car value used for tax),
- BIK percentage (set by emissions/fuel rules), and
- Your income tax band (20%, 40%, or 45%).
The core formula
1) Car taxable benefit
Car taxable benefit = P11D value × BIK rate
2) Car tax due
Annual car tax = Car taxable benefit × Your tax rate
3) Optional fuel benefit
If your employer also pays for private fuel, a separate benefit may apply:
Fuel taxable benefit = Fuel multiplier × BIK rate
Fuel tax = Fuel taxable benefit × Your tax rate
About the automatic BIK feature
When Auto-calculate BIK % is enabled, this tool uses a simplified emissions-based model:
- Electric cars are set to a low default BIK percentage.
- Hybrids with low CO₂ can use electric range bands.
- Higher emissions generally increase BIK progressively.
- Diesel may receive a supplement in this estimate model.
Because tax policy changes by year and jurisdiction, always confirm exact rates with your payroll team, accountant, or official guidance.
Worked example
Suppose your company car has a P11D value of £38,000, the BIK rate is 24%, and you are in the 40% tax band.
- Taxable benefit: £38,000 × 24% = £9,120
- Annual tax: £9,120 × 40% = £3,648
- Monthly tax: £3,648 ÷ 12 = £304.00
If private fuel is included, add fuel benefit tax on top of this amount.
Ways to reduce your company car tax
Choose lower-emission vehicles
In many systems, lower CO₂ means lower BIK rates. Electric and efficient hybrid cars often have a significant tax advantage.
Review optional extras
Factory options can raise the P11D value, increasing your taxable benefit.
Check fuel policy carefully
Company-paid private fuel can be expensive from a tax perspective. In some cases, paying for your own private fuel may be cheaper overall.
Common mistakes to avoid
- Using invoice price instead of P11D/list value.
- Forgetting private fuel benefit in calculations.
- Applying the wrong tax band.
- Assuming BIK percentages are the same each tax year.
Final note
This calculator is designed for planning and budgeting, not formal tax filing. Use it to compare vehicles, estimate payroll impact, and make smarter car-benefit decisions.