Enforcing employee to only avail only current leave balance

We have a requirement where employee can only avail leave based on their current balance as of today. The leave plan is incremental where 2 leaves are provided every month on a yearly basis. But when employee is applying for a future leave the system checks for projected balance and based on that allows employee to apply for a leave where in leave duration is more than the current balance.

For e.g. As of today i.e. 11 March 2025 employees has 4 days of leave.

Employee applies for Leave as of 01 April 2025. Since 2 days are given incrementally at the start of the repeating period the employee will have a potential balance of 6 days as of 01 April 2025.