If you work overtime you get paid more then the person who doesn't. Yes the tax man takes a slice but there are some deductions that are now available to you that the non-overtime worker isn't able to get. A few examples are a deductable meal for a notional sum up to a limit with no reciept. The use of personal vehicle as a deduction as public transport doesn't service the irregular hours, the transportation of business sensitive documents as well as the additional parking if paid to remain beyond normal hours. There is then the possibility of use of a home office and related expenses to service those hours. the 9-5er doesn't get to play these games.
