'What tax bracket am I in' and 'what percentage of my income goes to tax' sound like the same question, but in a progressive tax system with marginal brackets, they usually have very different answers. This mix-up leads to a common, incorrect worry: that earning slightly more money could push all of your income into a higher bracket and leave you with less take-home pay overall.
Marginal rate vs. effective rate
In a marginal-bracket system, each bracket's rate only applies to the slice of income that falls within that bracket, not your entire income. If you cross into a higher bracket, only the portion of income above that threshold is taxed at the higher rate -- everything below it is still taxed at the lower rates that applied to it. Your effective tax rate -- total tax paid divided by total income -- is a blend of all the brackets you passed through, and it is always lower than your top (marginal) bracket rate.
Where sales tax fits in
Sales tax is a separate, flat-rate tax applied at the point of purchase, calculated on the transaction amount, not your income. It doesn't interact with income tax brackets at all -- it's a completely different tax base, which is why a state or country can have a low income tax and a high sales tax, or vice versa, and comparing 'total tax burden' between two places means adding up several different tax types, not just one.
Using the right number for the right question
Use marginal rate to decide whether extra income (a raise, freelance work, overtime) is worth it -- it tells you how much of that specific next dollar you keep. Use effective rate to understand your actual overall tax burden for budgeting. Use sales tax rate for purchase-time cost estimates. The income tax bracket estimator and effective tax rate calculator show both numbers side by side so the difference is visible on your own income, not just in the abstract.