Does a raise ever reduce my take-home pay?

Not through federal brackets alone. You may lose means-tested benefits or credits, but the tax system itself never taxes an extra dollar at more than 37% federally.

What is the difference between a deduction and a credit?

A deduction reduces taxable income, so it saves your marginal rate multiplied by the amount. A credit reduces tax directly, dollar for dollar.

Do I need to file if I earn below the standard deduction?

Often not for federal income tax, but you may still want to file to claim refundable credits or recover withheld tax.

EarnAfterTax

Understanding US federal income tax

Brackets, standard deductions, FICA and filing status — a plain-English walkthrough of how a US federal tax bill is actually built.

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IRS — Rev. Proc. 2025-32 (2026 inflation adjustments)
IRS — Tax brackets and rates
IRS — Topic No. 751

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