How Tax Deductions Work: Standard vs Itemized and Common Examples

This article is for informational purposes only and does not constitute financial advice.

What Is a Tax Deduction?

A tax deduction is an expense or allowance that reduces a taxpayer\'s adjusted gross income (AGI) or taxable income, thereby lowering the amount of income subject to federal and, in most cases, state income tax. Deductions are distinct from tax credits: a deduction reduces the income on which tax is calculated, while a credit directly reduces the tax owed dollar-for-dollar. A $1,000 deduction is worth $220 to a taxpayer in the 22% marginal bracket, whereas a $1,000 credit saves $1,000 regardless of bracket.

The U.S. tax code contains two major categories of deductions: above-the-line deductions (available to all taxpayers regardless of whether they itemize) and below-the-line deductions (which require a choice between the standard deduction and itemized deductions).

Above-the-Line Deductions (Adjustments to Income)

Above-the-line deductions are subtracted from gross income to arrive at AGI. They are claimed on Schedule 1 of Form 1040 and are available whether or not the taxpayer itemizes. Common above-the-line deductions include:

• Student loan interest: Up to $2,500 of interest paid on qualified student loans, subject to income phase-outs.
• Educator expenses: Up to $300 ($600 for married educators filing jointly) for out-of-pocket classroom expenses.
• Health Savings Account (HSA) contributions: Contributions not made through payroll are deductible; the 2024 limit is $4,150 (self-only) or $8,300 (family).
• Self-employment taxes: Half of self-employment tax paid is deductible.
• Self-employed health insurance premiums.
• Alimony paid under pre-2019 divorce agreements.
• Traditional IRA contributions (if the taxpayer or spouse is not covered by a workplace plan, or income is below phase-out thresholds).

The Standard Deduction vs. Itemized Deductions

After calculating AGI, taxpayers choose between two options for below-the-line deductions: the standard deduction or itemized deductions. You may not claim both.

The Standard Deduction

The standard deduction is a flat amount set by the IRS, adjusted annually for inflation. The Tax Cuts and Jobs Act of 2017 nearly doubled the standard deduction starting in 2018, and as a result, roughly 87–90% of taxpayers now use it rather than itemizing. For tax year 2024, the standard deduction is:

Itemized Deductions

Taxpayers who have qualifying expenses totaling more than the standard deduction can itemize. Itemized deductions are reported on Schedule A and include specific categories defined by the tax code.

Common Itemized Deductions

State and Local Taxes (SALT)

The deduction for state and local taxes paid — including property taxes, state income taxes, or state/local sales taxes (but not both income and sales taxes) — is currently capped at $10,000 per return ($5,000 for MFS) under the TCJA. This cap significantly reduced the benefit of itemizing for taxpayers in high-tax states such as California, New York, and New Jersey.

Mortgage Interest Deduction

Interest paid on a qualified home loan is deductible on mortgage debt up to $750,000 (for mortgages originated after December 15, 2017) or $1 million for older loans. This deduction covers a primary residence and one second home. Points paid to originate a mortgage may also be deductible.

Charitable Contributions

Cash donations to qualified 501(c)(3) organizations are deductible up to 60% of AGI. Non-cash property donations (clothing, household goods) are deductible at fair market value up to 50% of AGI, with stricter limits for appreciated property donated to private foundations. Donations of appreciated securities held more than one year avoid capital gains tax on the unrealized gain and are deductible at full fair market value.

Medical and Dental Expenses

Out-of-pocket medical expenses that exceed 7.5% of AGI are deductible. Given the 7.5% floor, this deduction benefits primarily those with very high medical costs relative to their income — typically older taxpayers or those with significant unreimbursed expenses.

Casualty and Theft Losses

Since the TCJA, casualty and theft losses are deductible only if they result from a federally declared disaster. The loss must exceed $100 per event and the total must surpass 10% of AGI.

Comparing Standard vs. Itemized: Example

Bunching Deductions

A popular strategy for taxpayers who hover near the standard deduction threshold is to bunch multiple years of deductible expenses into a single tax year. For example, making two years of charitable contributions in one calendar year may push total itemized deductions above the standard deduction in the bunching year, while the taxpayer uses the standard deduction in the alternating year. Donor-advised funds facilitate this strategy by allowing a large upfront deduction while distributing grants to charities over time.

Business Deductions for the Self-Employed

Self-employed individuals and business owners can deduct ordinary and necessary business expenses on Schedule C (sole proprietors) or through their business entity. Common business deductions include home office expenses, vehicle mileage, professional subscriptions, health insurance premiums, and retirement plan contributions. The qualified business income (QBI) deduction under Section 199A also allows eligible pass-through business owners to deduct up to 20% of qualified business income.

Conclusion

Tax deductions are a central feature of the U.S. income tax system. Understanding the difference between above-the-line deductions, the standard deduction, and itemized deductions enables taxpayers to minimize their liability legally. Given the complexity of interactions between deductions, AGI phase-outs, and alternative minimum tax (AMT) exposure, individuals with complex financial situations often benefit from working with a qualified tax professional.