Depreciation is the accounting process of spreading the cost of a non-current asset over its useful life, to reflect the fact that it wears out or becomes obsolete. This matters for two linked reasons — and examiners test both:
- Depreciation is recorded as an expense on the income statement (reducing net profit), and
- It reduces the book value of the asset on the balance sheet (accumulated depreciation is subtracted from the asset's original cost).
The straight-line method (the only method required at SL, and the starting point at HL) charges the same amount each year:
Annual depreciation = (Cost − Residual value) ÷ Useful life
where residual (scrap) value is the amount the firm expects to sell the asset for at the end of its life, and useful life is the number of years the firm expects to use it.
Worked mini-example. A machine costs 50,000,hasaresidualvalueof5,000 and a useful life of 5 years.
- Annual depreciation = (50,000 − 5,000) ÷ 5 = $9,000 per year.
- After year 1 the book value = 50,000 − 9,000 = 41,000∗∗;afteryear2=∗∗32,000; and so on until it reaches the $5,000 residual value at the end of year 5.
Advantages of straight-line: simple, predictable, and good for assets that lose value evenly (e.g. buildings, fixtures). Limitation: it assumes even wear, which is unrealistic for assets like vehicles or technology that lose most value early on.