Cost of an asset at the start of the accounting period after deducting capital allowances given in earlier accounting periods. The closing written down value is the same as the opening written down value, less capital allowances given in the accounting period. This will be the opening written down value for the following accounting period. Where expenditure on plant and machinery is pooled for capital allowance purposes the closing written down value will be the opening written down value brought forward, plus any additional expenditure incurred, less any disposal proceeds, less any capital allowances given, and plus any balancing charges made.