Straight line basis is calculated by dividing the difference between an asset's cost and its expected salvage value by the number of years it is expected to be used.

To calculate straight line basis, take the purchase price of an asset and then subtract the salvage value, its estimated sell-on value when it is no longer expected to be needed. Then divide the resulting figure by the total number of years the asset is expected to be useful, referred to as the useful life in accounting jargon.

Straight Line Basis = (Purchase Price of Asset - Salvage Value) / Estimated Useful Life of Asset

Example scenario below

Assume that Company A buys a piece of equipment for $10,500. The equipment has an expected life of 10 years and a salvage value of $500. To calculate straight line depreciation, the accountant divides the difference between the salvage value and the cost of the equipment—also referred to as the depreciable base or asset cost—by the expected life of the equipment.

The straight line depreciation for this piece of equipment is ($10,500 - $500) / 10 = $1,000. This means that instead of writing off the full cost of the equipment in the current period, the company only needs to expense $1,000. The company will continue to expense $1,000 to a contra account, referred to as accumulated depreciation, until $500 is left on the books as the value of the equipment.

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