DBA calculation Query

Dear All ,

I am in the process of setting up DBA which has following requirement as follow -

An employee gets a monthly Basic Salary (X).

He has a DBA component (Y)

Y is not paid or deducted to/from the employee through payroll but calculated along with payroll.

At the end of a calendar year (December payroll) The Y amount should be 2.5 times the monthly basic salary [Y = 2.5 (X)]

Y is calculated monthly with year to date amount. Y is only for the finance team to have a forecast of the amount paid to the employee at the end of the year.