How Income Tax Works: A Plain-English Guide to Federal Taxes

In 2025, the federal tax brackets for a single filer are: 10% on income up to $11,925; 12% on $11,926–$48,475; 22% on $48,476–$103,350; 24% on $103,351–$197,300; 32% on $197,301–$250,525; 35% on $250,526–$626,350; 37% on income above $626,350.

A single filer with $80,000 of taxable income does NOT pay 22% on all $80,000. They pay: 10% on the first $11,925 ($1,193), 12% on the next $36,550 ($4,386), and 22% on the remaining $31,525 ($6,936). Total federal tax: $12,515. Effective rate: 15.6%. Marginal rate: 22%.

The marginal rate is the rate that applies to your next dollar of income — useful for decisions about Roth vs. Traditional IRA or 401(k) contributions. The effective rate is what you actually paid as a percentage of total income — useful for overall tax burden comparison.

The standard deduction for 2025 is $15,000 for single filers and $30,000 for married filing jointly. It reduces your taxable income dollar-for-dollar. Most people take the standard deduction because it's simpler and often larger than itemized deductions.

Itemized deductions include: mortgage interest, state and local taxes (SALT, capped at $10,000), charitable contributions, and unreimbursed medical expenses exceeding 7.5% of AGI. You should itemize if your total deductions exceed the standard deduction for your filing status.

Above-the-line deductions (available whether or not you itemize) include traditional IRA and HSA contributions, self-employed health insurance premiums, and student loan interest. These reduce your Adjusted Gross Income (AGI), which is the base for many other calculations.

Deductions reduce your taxable income. A $1,000 deduction saves you $220 if you're in the 22% bracket. Credits directly reduce your tax bill dollar-for-dollar. A $1,000 tax credit saves you $1,000 regardless of your bracket. Credits are almost always more valuable.

Common credits include the Child Tax Credit ($2,000 per qualifying child under 17), Earned Income Tax Credit (for lower-income workers, up to $7,830 for 3+ children), American Opportunity Credit (up to $2,500 for college tuition), and the Retirement Savings Contributions Credit.

Some credits are refundable (you get the excess as a refund even if you owe no tax), partially refundable, or non-refundable (only reduces tax to $0). The EITC is fully refundable — a major benefit for lower-income workers.

The biggest tax lever for most people is retirement contributions. Traditional 401(k) and IRA contributions reduce taxable income in the contribution year. Contributing $6,000 to a traditional IRA in the 22% bracket saves $1,320 in federal taxes. Roth contributions don't reduce current-year tax but grow tax-free.

Health Savings Accounts (HSAs) are the most tax-advantaged account type: contributions are pre-tax, growth is tax-free, and withdrawals for medical expenses are tax-free — a triple benefit. 2025 limits: $4,300 for individual coverage, $8,550 for family.

Tax-loss harvesting — selling investments at a loss to offset capital gains — can reduce your tax bill in taxable brokerage accounts. Up to $3,000 of net capital losses can be deducted against ordinary income annually, with remaining losses carried forward to future years.