Every car has a BIK percentage band. This is based on CO2 emissions, and a P11D value, which is the list price, including extras and VAT, but without the first year registration fee and vehicle tax.
To calculate the company car - or BIK - tax, multiply the P11D value by the BIK percentage banding, then multiply that figure by your tax band - i.e. 20% or 40%.
For a simpler way, use our Company Car Tax Calculator that will allow you to easily compare different cars against each other.