Both salary and commissions are taxable income. You report them on your tax return and your taxable income (after deductions and exemptions) are taxed according to your filing status and your tax bracket. So the short answer is that salary and commissions are taxed at the same rate.

How much will I get taxed on commission?

In case you are entitled for the commission, your commission should be paid through your salary and therefore it will be taxed with your salary itself, at the rate of 20%.

Why do I get taxed so much on commission?

regular wages is the way your employer withholds taxes. If your commission is being paid out as part of your weekly/bi-weekly salary then it is considered regular wages. ... IRS guidelines require employers to withhold tax at a 25% rate on top of withholdings for Social Security and Medicare taxes.