What is the double declining balance method of depreciation?

it's an accelerated depreciation method,

it calculates depreciation by applying a fixed percentage to the NET BOOK VALUE of the asset instead of historical cost less salvage value

this percentage is the double of the usual straight line method percentage

lets say an asset is depreciated on five years, the straight line depreciation applies 10% to the (historical less salvage) value

Double Declining method applies 20% to the NET BOOK VALUE of the asset until it reaches the salvage value