I think this is mostly a US thing. Why use yearly salary? You’re not paid once a year, are you? Most likely once a month. Referencing monthly salary makes much more sense.
“I’m making 50k”. Great, now I have to guess - dollars? Monthly? Yearly? If yearly then what’s the monthly paycheck? Net? Gross?
Because your yearly income dictates your tax bracket.
This isn’t how tax brackets work. Say we have 5%, 10%, and 15% in a system similar to the US with completely made up numbers. Say you make $99k, your first $33k will be taxed at 5% ($1650), your second $33k at 10%($3300), and your last $33k taxed at 15%($4950) totalling $9900. 9900/99000= a 10% effective tax rate. The real system is more complicated, but this is what it boils down to.
Nothing that I wrote conflicts with anything you said.
Being in Tax Bracket C doesn’t in any way imply you arent in Tax Bracket A.
The point is, Tax Brackets, and Taxes in general, are based on yearly income, so thats what people largely measure by once you are above a certain pay grade.
You get taxed by the year, so many people quote their income by the year, because its a quick and simple indicator of wealth/status.
You wrote “it determines your tax bracket” inferring you’d be in a single bracket and this is an extremely common misconception with how our tax system works. Furthermore, your income is only part of the equation since your tax rate is also affected by deductions, exemptions, and credits making two people making the exact same income can be taxed at different rates.
For future reference. Anytime people are talking about “their tax bracket” in a progressive tax system, they are talking about the top level bracket.
It’s typically redundant to, mid conversation, list all the tax brackets that exist under the one you’re talking about.