HMRC have produced a Ready Reckoner to calculate the rate of Writing Down Allowance for business expenditure on plant and machinery changed from April 2008 from 25 to 20 per cent for general plant and machinery and from 6 to 10 per cent for long-life plant and machinery. These changes were effective from 1 April 2008 for companies and 6 April 2008 for the self-employed, or people in partnerships

In order to ensure a fair and equitable transition to the new rates, a business whose chargeable period (that is, its period of account or accounting period) spanned the relevant change date, must use a hybrid rate of WDA for that transitional period only.

The Ready Reckoner tool includes instructions which tell the user what information to input. Essentially, the user is asked to insert the dates of the transitional chargeable period and the type of WDA for which a hybrid rate is needed.

The Ready Reckoner will respond with an appropriate message if a user inadvertently inputs incorrect information, such as dates for a period that is not, in fact, a transitional chargeable period.

Full details of the transitional measures and ready reckoner is available at http://www.hmrc.gov.uk/capital_allowances/read-reck-intro.htm