The cost principle is one of the basic underlying guidelines in accounting. It is also known as the historical cost principle.

The cost principle requires that assets be recorded at the cash amount (or its equivalent) at the time that an asset is acquired. For example, if equipment is acquired for the cash amount of $50,000, the equipment will be recorded at $50,000. If the equipment will be useful for 10 years with no salvage value, the straight-line depreciation expense will be $5,000 per year (cost of $50,000 divided by 10 years). The equipment's market value, replacement cost or inflation-adjusted cost will not affect the annual depreciation expense of $5,000. The company's balance sheets will report the equipment's historical cost minus the accumulated depreciation.

The cost principle also means that valuable brand names and logos that were developed through effective advertising will not be reported as assets on the balance sheet. This could result in a company's most valuable assets not being included in the company's asset amounts. (On the other hand, a brand name that is acquired through a transaction with another company will be reported on the balance sheet at its cost.)

If a company has an asset that has a ready market with quoted prices, the historical cost may be replaced with the current market value on each balance sheet. An example is an investment consisting of shares of common stock that are actively traded on a major stock exchange.