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Glossary

Tax Base

A tax base is the amount of income, property, or transaction value that a tax is actually calculated on, after any allowed exclusions, deductions, or adjustments are taken into account.

What Is a Tax Base?

A tax base is the figure to which a tax rate is applied. If a tax is a percentage charge, the tax base is the number that percentage is multiplied by. Governments define the base separately for each tax, so the same asset or income can have different tax bases under different taxes. For example, income tax is usually charged on taxable income, while property tax is usually charged on an assessed value of real estate.

The tax base is not always the same as the money a person earns or owns. Tax law often starts with a gross figure and then subtracts allowed deductions or exemptions. The result is the base that the rate is applied to.

How the Tax Base Is Calculated

The basic relationship is:

Tax owed = Tax base × Tax rate

For a capital gains tax, the base is usually the gain on an asset, meaning the sale proceeds minus the cost basis. Cost basis is generally the purchase price plus certain costs, such as commissions or qualifying improvements, and it can be adjusted over time for events like depreciation or stock splits. The exact rules vary by country and by asset type, so the definition in the relevant law matters.

Why It Matters to Investors

Because the tax base determines the taxable amount, small differences in how it is defined can change a tax bill considerably. Investors often encounter tax bases when tracking the cost basis of shares, when comparing the assessed value of a property with its market price, or when reading about proposed tax changes that broaden or narrow the base. A broader base at the same rate generally raises more revenue, while a narrower base with more exemptions reduces the amount taxed. Keeping accurate records of purchase prices and adjustments makes it easier to determine the base when an asset is sold.

Updated October 21, 2026. For general education only; not financial, tax or legal advice.

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Related Terms

Income Tax

Income tax is a tax that governments levy on the money individuals and businesses earn, such as wages, interest, dividends, and profits, usually calculated as a percentage of that income.

Property Tax

A property tax is a recurring tax levied by a government on the value of real estate, such as land and buildings, that property owners pay to fund local public services.

Capital Gains Tax

A capital gains tax is a tax on the profit made when an asset, such as a stock, bond, or property, is sold for more than its original purchase price.

Cost Basis

Cost basis is the original value of an asset for tax purposes, usually its purchase price plus certain costs, used to work out the capital gain or loss when the asset is sold.

Depreciation

Depreciation is the accounting method of spreading the cost of a tangible, long-lived asset over the years it is expected to be used, recording a portion as an expense each year.

Taxable Income

Taxable income is the portion of a person's income that remains after allowable deductions and exemptions, and it is the amount on which income tax is actually calculated.

Assessed Value

The value a local government assigns to a property, or other taxable asset, as a basis for calculating property taxes. It is often different from the price the asset would sell for.

Effective Tax Rate (ETR)

The effective tax rate is the average percentage of a person's or company's total pre-tax income that is actually paid in taxes, as opposed to the statutory or marginal rate.