How to calculate and record monthly paid time off ( vacation and sick leave) expenses?

I find out that it is confusing to calculate employees' paid time off expenses on 12/31 and 1/31 of each year. For example: On 12/31/2018, employee A used $100.00 vacation, had $100.00 unused vacation benefit remaining to be carried over to 2019. Employee A also used $50.00 sick leave benefit, had $50.00 sick leave benefit remaining. However, company would forfeit this $50.00 unused sick leave benefit. Question: What is the total amount of paid time of expenses of employee A on 12/31/2018? We currently link payroll vacation benefit to a liability account and sick leave benefit to an expense account. Thank you! A QuickBooks user