Understated

When an amount is reported at less than its' actual value it is said to be 'understated'. This can be of beneficial purpose in business such as profit projections being on the cautious side.

Specific to UK tax returns, an understatement will generally be an error that subsequently needs 'amending' with a revised filing. It is possible, for instance, to 'understate' either income or expenses, accordingly affecting the tax calculation and this will need correcting.