Is it possible to calculate overtime hours without actually entering it in system?

The user base wants the system to calculate any hours spent on project more than the set number to be automatically calculated as 'Overtime'.

If in calendar if a week is for 8 days per day for 5 days then the total number of hours a person has to work on a week is 40. If anyone .has worked 45 hours then the 5 hours should be automatically calculated as overtime and accounted in Project Costing as such

Thanks

Atul