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An official reduction or elimination of one’s assessed valuation after completion of the original assessment. Also, defined as an official reduction or elimination of one’s tax liability after completion of the tax roll.

​​​​​​​Actual value

The value used pursuant to Colorado Revised Statutes for ad valorem or property tax purposes. Actual value is often synonymous with market value. Actual value is determined by considering the cost, market, or income approaches to value. Colorado Revised Statutes defines or determines the specific method or procedure used, depending on the type/class of property.

​​​​​​​Ad valorem taxation

A tax levied in proportion to the value of the thing (s) being taxed. In Colorado, the property tax is an ad valorem tax.


A legal process in which a property owner contests a value or assessment either formally or informally on taxable real or personal property. For each year, there are specific statutory dates when an appeal can be made.


The act or process of developing an opinion of value; an opinion of value.

Appraisal date

For assessment purposes in Colorado, property is valued based upon how it physically exists as of January 1 of each year. However, the value is based on a retrospective appraisal date ending June 30th of an even-numbered year for each reappraisal cycle.


One who is expected to perform valuation services competently and in a manner that is independent, impartial, and objective. Appraiser employees in Colorado assessor offices must be registered, licensed, or certified within two years of hire, per Colorado Statutes.

Assessment date

The assessment date in Colorado is twelve noon January 1 of each year. This date is often referred to as the lien date. See "Lien Date."

Assessment or assessed value

The percentage of actual value (market value) that is subject to taxation. Assessed value equals the actual value multiplied by the statutory assessment rate. Example: $129,000 actual value x 6.7% assessment rate = $8,640 assessed value, (rounded.) This amount is subject to tax when multiplied by a mill levy.

Assessment rate

A statutory rate or percentage that is multiplied times the actual value of the property.  This results in the assessed value for property tax purposes.

Property Classes and Subclasses Updated 2023 per SB23B-001_0.pdf


The elected official responsible for discovering, listing, and valuing all real and taxable personal property within the county.


The Assessor generates a Certification of Value for each taxing entity. The information within the Certification helps each district calculate their annual mill levy. The Certification of Values is completed twice each year, August 25th and no later than December 10th, unless extended by the legislature.

Economic area

Typically, an Economic Area is comprised of a group of neighborhoods the Assessor studies together during the mass appraisal in order to attain statistical performance.


All property in Colorado is taxable unless specifically exempt by statute. Most all property owned by Federal, State, and Local governments is statutorily exempt. Other exemptions may be granted to owners of property operated for religious or charitable purposes.

Geographic Information System (GIS)

A database management system used to store, retrieve, manipulate, analyze, and display spatial (map) information.


A term used to describe all buildings, structures, pools, fences, etc., fixed to the land.

Intervening year

A term used exclusively in Colorado for property taxation which refers to the year between mandated reappraisal years. Colorado is on a two-year cycle, the first year being the Reappraisal Year and the second year the Intervening Year. The Intervening Year occurs during even-numbered calendar years.


The date that the property tax bill attaches to a property and the property becomes security for the lien.

Mass appraisal

The process of valuing a universe of properties as of a given date using standard methodology, employing common data, and allowing for statistical testing. This mass appraisal methodology is used in property tax assessments

Mill levy

A rate used to calculate the property tax bill sent to an individual property owner. The levy or mill levy can be converted to a decimal, then multiplied by the assessed value to calculate the taxes due. Conceptually, a mill levy is some number (x) over 1,000. So, it can be converted to a decimal by dividing the total mill levy by 1,000: 87.925 / 1,000 = .087925. Then, if a property has an assessed value of $15,000, the tax would be $ 1,318.87: $15,000 x .087925 = $1,318.87.


A group of complimentary land uses with similar houses, buildings, or businesses.

Notice of Valuation (NOV)

An official document notifying the owner of the proposed actual and/or assessed valuation. Notices of Valuations are mailed on or before May 1st of each year.

Personal property

Consists of every kind of property that is not real property. Personal property typically can be moved without damage to itself or real estate. Personal property is typically divided into tangible and intangible. In Colorado it usually refers to movable items not permanently affixed to, or part of, the real estate and is commonly known as “personalty" or "chattels."

Possessory interest

A taxable interest in land owned by a governmental entity that is leased to a private owner for non-residential use. Examples may include grazing leases on BLM land, ski runs on Forest Service land, private hangars on ground leased at a public airport, restaurant seating on a public sidewalk, etc.


Consists of the interests, benefits, and rights inherent in the ownership of land plus anything permanently attached to the land or legally defined as immovable. It is also considered as "real estate" which commonly includes land and any improvements. Often referred to as "realty."

Property tax

A tax levied on property. In Colorado, property tax is an ad valorem tax in proportion to the value. See "Ad Valorem Taxation"

Real property

Refers to the interest, benefits, and rights inherent in the ownership of physical real estate

Reappraisal year

A term used in Colorado which refers to the mandatory year in which all property must be valued or reappraised for property tax purposes. Reappraisal years occur during each odd-numbered calendar year.

Special assessments

Direct charges which are against the property, but not included in the Assessor’s valuation. For example, alley improvements, irrigation water, etc.

Tax base

Total assessed value in a given tax district or taxing authority.

Tax rate

Rate in dollars which when applied to each $1,000 of assessed value will give the tax amount. Rates vary from one district to another depending on the tax base and the needs of the people in that district or jurisdiction.

Tax warrant or tax roll

A compilation or summary of all taxable real and personal property and its value. The tax roll typically includes, name, address, legal, assessed values, levy, and other pertinent information.

Tax year

Most governmental jurisdictions or taxing authorities operate on a calendar year basis. The calendar year begins January 1 and ends December 31 of each year.

Uniform Standards of Professional Appraisal Practice (USPAP)

A publication by the Appraisal Standards Board of the Appraisal Foundation. Both appraisers and users of appraisal services use USPAP as an authoritative reference regarding ethical and performance obligations. The Colorado Board of Appraisers adopted USPAP, and uses it as a reference when enforcing complaints against licensees