The tax amount is linked to the category you have selected. The default allowable tax amount is set to 100% for all Income and Expense categories, with the exception of ‘Entertainment’, which is defaulted to 0%. So if you change the category to or from ‘Entertainment’, the allowable tax amount will also change. However, if you’ve entered a specific allowable tax amount in the Tax module, this amount will stay the same, even if you change the category.