A deduction from a taxpayer's taxable adjusted gross income that is made up of deductions for money spent on certain goods and services throughout the year. The specific deductions that are allowed are outlined by the Internal Revenue Service and include such expenses as mortgage interest, state and local taxes, gifts, and medical expenses.

Usually, an itemized deduction is limited to a certain percentage of adjusted gross income. As an alternative to standard deduction, an itemized deduction requires taxpayers to keep track of each possible tax-reducing expense throughout the year.

Individuals who frequently spend large amounts on medical care, state and local taxes, donations or other deductible expenses may be better off itemizing. However, tax law may set thresholds in spending that must be exceeded before the deductions can be made. For example, in the medical category, perhaps only expenses that exceed 7.5% of your adjusted gross income may be deducted. If you didn't spend at least that much, then none of your medical expenses will be deductible.