Can a raise make all income taxed at a higher rate?

No, not under ordinary progressive bracket mechanics. A higher bracket applies to the next layer of taxable income, not all prior income.

Original example:

• Devon Hart has 49,200 of taxable income.
• A simplified rate table taxes the next layer above 50,000 at a higher rate.
• Devon receives a 1,500 bonus.

Only the part of the bonus that crosses the bracket line is taxed at the higher marginal rate. The income already inside the lower brackets stays taxed under those lower layers.

The exam distinction is:

• marginal rate: rate on the next dollar or next layer
• effective rate: total tax divided by total income measure

Be careful: real-life benefit cliffs, credits, phaseouts, and state rules can create separate effects. But a federal bracket crossing by itself does not tax all income at the highest rate.