Income and Payroll Taxes Explained: Marginal Rates, Effective Rates, FICA, Capital Gains, and More
Taxes touch every dollar you earn, save, or sell an asset for — yet the underlying rules are frequently misunderstood. Most confusion comes from conflating marginal and effective rates, overlooking payroll taxes, or not accounting for the difference between ordinary income and capital gains. This guide builds a clear mental model of how the US tax system works and shows you how to estimate your liability in each category.
Marginal vs Effective Tax Rate
The US federal income tax is progressive: income is taxed in brackets, each portion taxed at its own rate. Your marginal rate is the rate applied to the last dollar of income you earned. Your effective rate is the total tax paid divided by total taxable income.
| 2025 Tax Bracket (Single) | Rate |
|---|---|
| $0 – $11,925 | 10 % |
| $11,926 – $48,475 | 12 % |
| $48,476 – $103,350 | 22 % |
| $103,351 – $197,300 | 24 % |
| $197,301 – $250,525 | 32 % |
| $250,526 – $626,350 | 35 % |
| Over $626,350 | 37 % |
Someone earning $80,000 is in the 22 % marginal bracket but pays an effective rate well below 22 % because the lower brackets apply to the first portions of income. The Marginal Tax Bracket Calculator shows which bracket each slice of income falls into, and the Effective Tax Rate Calculator computes the blended overall rate.
Payroll Taxes: FICA
FICA (Federal Insurance Contributions Act) taxes fund Social Security and Medicare and apply to earned income regardless of your income tax bracket:
| Component | Employee rate | Employer rate | Wage base (2025) |
|---|---|---|---|
| Social Security | 6.2 % | 6.2 % | $176,100 |
| Medicare | 1.45 % | 1.45 % | No cap |
| Additional Medicare | 0.9 % | 0 % | Wages > $200,000 (single) |
Employees see 7.65 % withheld from paychecks (up to the Social Security wage base). The employer matches this, meaning the full FICA cost is 15.3 % of wages. The FICA Tax Calculator breaks down exactly how much is withheld at any income level, and the Payroll Tax Calculator computes the employer cost side of the ledger.
Self-Employment Tax
Self-employed individuals pay both the employee and employer share of FICA, totalling 15.3 % on net self-employment income up to the Social Security wage base (12.4 % Social Security + 2.9 % Medicare). However, you may deduct half of the self-employment tax as an above-the-line deduction, reducing your taxable income:
SE tax = net SE income × 0.9235 × 0.153
The 0.9235 factor accounts for the employer deduction. The Self-Employment Tax Calculator computes both the SE tax owed and the deductible amount.
Capital Gains Tax
Investment gains are taxed differently from ordinary income. The rates depend on holding period:
- Short-term capital gains (held ≤ 1 year): taxed at ordinary income rates (up to 37 %).
- Long-term capital gains (held > 1 year): taxed at preferential rates of 0 %, 15 %, or 20 % depending on taxable income.
An additional 3.8 % Net Investment Income Tax (NIIT) applies to investment income for single filers above $200,000 MAGI. The Capital Gains Tax Calculator determines whether your gain qualifies for long-term rates and computes the tax at the appropriate rate including any NIIT.
Take-Home Pay and Paychecks
Gross pay is reduced by federal income tax withholding, FICA, state income tax, and any pre-tax benefit deductions (401k contributions, health insurance premiums, FSA elections). The result is your net (take-home) pay. The Paycheck Take-Home Calculator models all of these reductions for any pay period and filing status. The Gross-to-Net Salary Calculator does the same for annual salary comparisons. Bonuses may be withheld at the IRS supplemental flat rate of 22 % (or 37 % above $1 million) rather than your regular withholding rate — the Bonus Tax Withholding Calculator explains both methods and their true tax costs.
Quarterly Estimated Taxes
If you are self-employed, receive significant investment income, or have other income not subject to withholding, you must make quarterly estimated tax payments to avoid an underpayment penalty. The IRS safe-harbour rule requires paying either:
- 100 % of last year's tax liability (110 % if last year's AGI exceeded $150,000), or
- 90 % of the current year's expected tax liability
The Quarterly Estimated Tax Calculator computes each quarter's payment due date and recommended amount.
Property Tax and VAT
Property tax is levied by local governments, typically as a mill rate applied to assessed value: tax = assessed value × mill rate / 1,000. Rates vary enormously by state and county. The Property Tax Calculator converts mill rates to annual dollar amounts and lets you compare tax burden across locations. For businesses selling goods or operating in VAT-governed jurisdictions, the VAT Calculator isolates the tax component from a VAT-inclusive price or adds VAT to a net amount.
Common Mistakes
- Fearing that a raise will cause you to pay more tax on all your income. Only the portion of income above a bracket threshold is taxed at the higher rate. A raise never results in lower take-home pay due to taxes alone.
- Forgetting self-employment tax when estimating freelance income. Adding the 15.3 % SE tax to income tax obligations often surprises new freelancers. Always factor it in when pricing services.
- Selling appreciated assets before the one-year mark. Waiting an extra day or week to cross the long-term holding threshold can cut the tax rate on a gain by more than half.
- Under-withholding on a bonus. If your bonus is withheld at 22 % but your marginal rate is 32 %, you will owe the difference at filing.
What is the difference between a tax deduction and a tax credit?
A deduction reduces your taxable income; its value depends on your marginal rate. A $1,000 deduction saves you $220 in the 22 % bracket. A credit reduces your tax bill dollar for dollar; a $1,000 credit saves $1,000 regardless of your bracket. Credits are therefore more valuable per dollar.
Do I need to pay estimated taxes?
You generally must pay quarterly estimates if you expect to owe at least $1,000 in federal tax after subtracting withholding and credits, and if withholding plus credits will cover less than 90 % of your current-year tax or 100 % of last year's tax. W-2 employees with side income often fall into this category.
How does the Additional Medicare Tax of 0.9 % work?
Employers withhold the additional 0.9 % on wages over $200,000 (for a single employee), but the threshold is based on combined household income for married filers ($250,000 MFJ). If two spouses each earn $175,000, no employer withholds the surcharge, but they owe it at filing. The FICA Tax Calculator flags this scenario.