All would be automatically by our end. Just applying for leave as usual & make sure your carry forward balance hasn't expired yet. We would compare and calculate the duration to be deducted from the carry forward leave balance. If the carry forward balance is insufficient, we would deduct the remaining duration from your current year's balance.

Let's say you have 

-5 days of carry forward leave,

-2 days of current year's balance.

You have applied for leave with 6 days duration. 

After applying, your 

-carry forward balance left 0 days

-current year's balance left 1 day.

The same logic applies when the approver updates your leave duration to either longer or shorter, we would always prioritize the carry forward balance. If insufficient, we would deduct it from the current year's balance.