The book value of an asset, also called its carrying value, is the amount at which the asset is recorded on the balance sheet after subtracting whatever accumulated depreciation, depletion, or amortization has been recognized against it since it was acquired. For a tangible asset it is original cost minus accumulated depreciation; for a depletable natural resource it is cost minus accumulated depletion; for an amortizable intangible asset it is cost minus accumulated amortization.
Why book value changes over time
Book value starts at an asset's original acquisition cost and declines steadily each period as depreciation, depletion, or amortization expense is recognized, continuing until the asset is either fully written off, sold, or retired. The pattern of decline depends entirely on which depreciation method is used: straight-line depreciation reduces book value by an equal amount each period, while an accelerated method such as declining balance reduces it faster in the early years and more slowly later on.
Book value versus fair market value
Book value is explicitly not intended to represent what an asset is currently worth in the market. A building purchased decades ago may have a very low remaining book value due to years of accumulated depreciation, while its actual market value, driven by rising real estate prices, could be many times higher. Conversely, specialized equipment can lose market value far faster than its scheduled depreciation reflects, leaving a book value well above what the asset could actually be sold for. This gap between book value and market value is exactly what an impairment test is designed to catch when it becomes significant and permanent.
Book value at disposal
When an asset is sold, its book value at the date of sale is compared against the proceeds received: if proceeds exceed book value, the company recognizes a gain; if proceeds fall short, it recognizes a loss. This comparison, not a comparison against the asset's original cost, is what actually determines the gain or loss on sale recorded on the income statement.
Why the concept matters despite its limitations
Even though book value is not a market value estimate, it remains central to financial reporting because it is objective, verifiable, and consistently calculated under the cost principle, giving readers of the financial statements a stable, auditable figure rather than a constantly shifting market estimate for every asset a company owns, however imperfectly that figure may track true economic worth at any given moment.
A simple worked example
A machine purchased for $80,000 with $50,000 of accumulated depreciation has a book value of $30,000. If the company sells it for $35,000, it recognizes a $5,000 gain; if it instead sells it for only $22,000, it recognizes an $8,000 loss — in both cases the gain or loss is measured against the $30,000 book value, not the original $80,000 purchase price.
Book value is not market value
One of the most persistent misunderstandings in accounting is treating an asset's book value as an estimate of what it could actually be sold for today. Book value is a purely mechanical result of applying an accounting cost allocation method, and it can sit well above or well below current market value depending on how an asset's real-world value has moved since purchase — a building in a rapidly appreciating neighborhood can carry a book value far below what it would fetch on the open market, while specialized equipment can easily be worth less than its book value once a buyer actually tries to sell it. Analysts who need a market-based figure instead look to appraisals, comparable sales, or fair market value estimates rather than relying on the balance sheet's book value figure.