Which rate should I use for a side project?+
The marginal rate, because incremental income stacks on top of what you already earn and is taxed at the highest band it reaches.
Can a raise ever leave me worse off?+
Not from brackets alone, because only the income above a threshold is taxed at the higher rate. It can happen through benefit or credit cliffs that phase out sharply, which brackets have nothing to do with.
Why is my effective rate so much lower than my bracket?+
Because earlier income is taxed at the lower bands and deductions come off before any of it. Only the last slice of income is taxed at your top rate.
Should the effective rate include payroll tax?+
It depends what you are measuring. Income tax alone gives a lower number, and adding Social Security and Medicare gives a fuller picture of the tax on your earnings. Be consistent when comparing across years.
Are these numbers financial advice?+
No. They are educational estimates based on the inputs and assumptions on this page. Confirm important decisions with a qualified professional and your own documents.