I refer to the letter Non-Muslims paying 'jizyah' tax by Puspha Lingam and Dhimmitude in Malaysia? by Paul Warren.

The calculation of payable zakat in Malaysia now, as adopted by many of the state Islamic councils and Zakat Collection Centres (PPZ) is at 2.5 percent of the net income after allowable deductions just as in our income tax.

When a zakat payment is made, it is the same as paying 2.5 percent of the tax. Please refer here for further information. There are many other forms of zakat and I hope the preceding link will be able to clarify any misunderstandings.

In the case of charity, the same rule applies i.e. they are to be deducted from the gross income. This is because they are no obligations for charity. Zakat, on the other hand, is obligatory, and the calculation method is the same as that for income tax.