To the right of each coding line on the Coding tab, you will see a Tax Code field. When you click the field's drop-down you will see the tax codes available to you for this transaction. The tax codes that appear depend on what country you made the purchase in, and on your company taxation policies in that country. Once a tax code is selected, the transaction's tax amount is automatically worked out for you.
A tax calculator (accessed by clicking to the right of the Tax Code field) gives you the ability to define (split) a tax amount across more than one line. This calculator is particularly useful for international transactions or transactions with split amounts of taxation.
To split the transaction's tax amount across more than one coding line:
Note: If the transaction is not an international transaction or the tax code selected for the transaction line is a zero-rated tax code, some of the fields will be greyed out.