Estimate Your Company Car Tax
Use this calculator to estimate employee Benefit-in-Kind (BIK) tax and employer Class 1A National Insurance on a company car.
A company car can be a valuable perk, but it also comes with tax implications for both the employee and the employer. If you're trying to decide whether a company car is worth it, understanding Benefit-in-Kind (BIK) tax is essential.
What is company car tax?
Company car tax is the tax paid when an employee is allowed to use a work vehicle for private journeys. HMRC treats this private use as a taxable benefit. The amount taxed is called the car benefit and is usually calculated using:
- The vehicle’s P11D value
- The official BIK percentage
- The employee’s income tax rate
Employers also pay Class 1A National Insurance on the taxable benefit.
How this calculator works
This calculator estimates your annual and monthly company car tax by applying a BIK percentage based on fuel type, CO₂ emissions, electric range (for low-emission cars), and tax year.
Inputs used
- P11D value: Starting valuation of the car for tax purposes.
- CO₂ emissions: Lower emissions generally reduce BIK tax.
- Fuel type: Diesel cars may attract a supplement.
- Electric range: Relevant for certain plug-in hybrid bands.
- Income tax band: 20%, 40%, or 45%.
- Employee contribution: Can reduce taxable benefit.
- Fuel benefit: Optional extra tax if private fuel is provided.
Core formula (simplified)
1) Find taxable car benefit
Taxable Car Benefit = (P11D Value × BIK %) − Employee Contributions
2) Find employee company car tax
Employee Tax = Taxable Car Benefit × Income Tax Rate
3) Find employer NIC
Employer Class 1A NI = Taxable Car Benefit × NI Rate
4) Add fuel benefit if applicable
If private fuel is covered by the employer, a separate fuel benefit charge is multiplied by the same BIK rate and then taxed.
Worked example
Suppose your car has a P11D value of £42,000, a BIK rate of 15%, and you are a 40% taxpayer:
- Taxable car benefit = £42,000 × 15% = £6,300
- Employee tax = £6,300 × 40% = £2,520 per year
- Monthly equivalent = £210
If fuel benefit is included, your total annual tax can rise significantly, especially at higher tax bands.
How to reduce your company car tax
- Choose low-emission or fully electric vehicles.
- Compare company car vs. car allowance before choosing.
- Consider whether employer-paid fuel is actually good value.
- Check your tax code after receiving a company car.
- Track employee contributions and ensure payroll applies them correctly.
Company car vs cash allowance
There is no universal winner. A company car can be tax-efficient for electric vehicles and convenient for maintenance, insurance, and fleet support. A cash allowance may offer flexibility but shifts ownership risk, depreciation, and admin to the employee.
The best approach is to compare:
- Net take-home pay impact
- Total running costs
- Business mileage reimbursement
- Insurance and servicing responsibilities
Frequently asked questions
Is this calculator 100% HMRC accurate?
It is designed as a planning tool and uses practical assumptions. For payroll and tax filings, always verify current HMRC rates and detailed rules.
Why are electric cars often cheaper for BIK tax?
Because they typically have much lower BIK percentages, which reduces the taxable benefit and the resulting employee tax bill.
Does diesel always cost more?
Not always, but a diesel supplement often applies unless specific emissions criteria are met.
Final thoughts
A clear company car tax estimate helps employees avoid surprises and helps employers budget total compensation costs. Use the calculator above to test realistic scenarios, then confirm final figures with your payroll team or tax adviser before making a decision.