In finance, a straight-line basis is a method for calculating depreciation and amortization. It is calculated by subtracting an asset's salvage value from its current value and dividing the result by the number of years until it reaches its salvage value.

If the results of calculating the basis were graphed, it would appear as a straight line, hence the name. The straight-line basis is the simplest way to determine the loss of value of an asset over time.