working out benefits in kind

Thats 20% x (Market Value) for each year the computer has been kept. And if the asset - in this case the computer - is given to an employee then use this formula to work out the assessable amount to add to their income:

(Original Market Value of asset when first provided) - [20% X (Market Value) x Number of years asset is kept up to the purchase date] - (Amount paid by employee if bought)

Ignore the Market Value at the time of the purchase as this is not required.