Percentage of annual commission deducted

I am in sales and earn a commission at the end of the year. I would like to ascertain how much of that I will be losing to tax. Is there a formula or a percentage?

The commission will get added to your salary and taxed at your marginal rate of tax according to the normal tax tables. If your commission is greater than 50% of your salary, then there are certain expenses you can deduct against the commission to reduce your tax liability.