Leave entitlement Validation.

Hi Experts,

My client has 2.5 days Earned Leave for a month. But the condition is this 2.5 days can be earned only when the employee's previous months attendence is full month. Otherwise the limit of Erned leave will be calculated like "(Total Days present/ Total days of month)* 2.5 days. How and where should I validate it?

Nasim haider