How home valuation tools work

AVM, CMA, or reasoned valuation: what each delivers

8 min read

Four ways to put a number on a home, what each one is for, and the blind spot built into each.

The short version

There are four common ways to value a home, and they are not interchangeable. An AVM gives an instant algorithmic estimate. A CMA is an agent's comparative analysis using selected comparables and local knowledge. A reasoned valuation states a number alongside the comparables and an honest range, showing its work. An appraisal is the licensed, in-person figure a lender will accept. Each answers a different question, and the mistake is treating one as a substitute for another.

The four methods at a glance:

Method	What it is	Who produces it	Cost	Main limit
AVM	Instant estimate from records and comps	Software, such as Zillow or Redfin	Free	No inspection; about 7.5% off-market error
CMA	Agent comparison using selected comps and local knowledge	A real estate agent	Usually free	Varies by agent; not certified
Reasoned valuation	A number with the comps, reasoning, and an honest range shown	Software plus method	Free	Not an appraisal; not MLS-connected
Appraisal	Licensed in-person valuation a lender accepts	A licensed appraiser	$300 to $600	Slow; tied to a transaction

The AVM: instant, free, and unaware of the home

An automated valuation model returns a number in seconds from public records and comparable sales. It costs nothing, covers nearly every home, and is reasonable where data is dense. Its structural limit is that no one looked at the property: it cannot see condition, recent work that never hit the record, or the feel of a street. Accuracy reflects that, near 2% median error for listed homes, but about 7.5% for off-market ones on Zillow and roughly 6% to 7% on Redfin. It is a fast first read, not a verdict. (For how it is built and where it breaks, see how AVMs work.)

The CMA: human judgment, variable and uncertified

A comparative market analysis is what an agent prepares for a listing. The agent selects comparable sales, adjusts for differences a database cannot weigh, and brings in what they know about the block, the buyer pool, and current demand. It is usually free, and it carries real human judgment, the thing the AVM lacks. Its limits are the mirror image: it is not a certified valuation, its quality varies with the agent, and because it often doubles as a listing pitch, it can lean optimistic. Two agents can hand the same seller two different numbers, and neither is wrong on paper.

The reasoned valuation: the number with its work shown

A reasoned valuation sits between the speed of the AVM and the judgment of the CMA. It returns a number, but it also shows the comparables it used, the reasoning behind the figure, and an explicit confidence range, and it names what it cannot see. The point is not a more confident number; it is a more honest one. Where an AVM hides its uncertainty behind a single figure, a reasoned valuation puts the uncertainty on the page, because the true answer to "what is this worth" is a range, not a point. This is the approach behind our home-value page. Its limits are worth stating plainly: it is not a licensed appraisal, and it is not connected to your local MLS, so an agent with live MLS access and eyes on the home still sees more.

The appraisal: authoritative, slow, and transaction-bound

A licensed appraisal is the only valuation a lender, a court, or the IRS will treat as authoritative. A state-licensed appraiser inspects the home in person, selects comparables, and makes manual adjustments, and the result governs mortgage lending. It costs roughly $300 to $600 for a standard home, more for complex ones, and it is slow and tied to a transaction. It is the most reliable single number and the least convenient: you cannot run one every time you are curious.

The real difference: how each treats uncertainty

The four methods differ most in honesty about what they do not know. The AVM is the most confident and the least transparent: one number, no inspection, uncertainty buried. The appraisal is authoritative but only available at the moment of a transaction. The CMA brings human judgment but varies by who makes it and is not independently checkable. The reasoned valuation tries to keep the AVM's speed while showing its work and its limits. None of them replaces a physical inspection of a specific home in a specific market, which is why the most useful number usually comes from combining them rather than trusting one.

What this means for an agent

When a seller opens with a Zestimate, the productive move is not to argue the figure. It is to explain which kind of valuation it is, an instant AVM with a known off-market error and no eyes on the home, and to show what your own analysis sees that the model cannot. Naming the category, and the blind spot that comes with it, reframes the conversation from "your number versus mine" to "here is how each number was built." For the consumer-facing version of this comparison, see CMA, appraisal, or AVM, and for why the single number is the core problem, see what confidence should mean in a valuation tool.

Frequently asked questions

What is the difference between an AVM and a CMA?

An AVM is an instant algorithmic estimate from public records and comparable sales, with no inspection of the home. A CMA is a comparative market analysis prepared by an agent who selects comparables and applies local knowledge. The AVM is fast and consistent but cannot see condition; the CMA carries human judgment but varies by agent and is not certified.

Is a Zestimate the same as an appraisal?

No. A Zestimate is an AVM, an automated estimate that cannot be used for lending and has a median error near 7.5% for off-market homes. An appraisal is performed in person by a licensed appraiser, costs roughly $300 to $600, and is the only valuation a lender, court, or the IRS will accept as authoritative.

What is a reasoned valuation?

A reasoned valuation states a home's value along with the comparables used, the reasoning, and an explicit confidence range, and it names what it cannot see. It keeps the speed of an AVM while showing its work, so the uncertainty is on the page rather than hidden behind one confident number.

Which home valuation is most accurate?

A licensed appraisal is the most reliable single number, but it is slow and tied to a transaction. For everyday use, combining methods works best: an AVM for a fast baseline, recent comparable sales, and an agent's analysis for condition and demand. No single automated number captures a specific home in a specific market.

Why do two agents give different CMA numbers?

A CMA involves judgment: which comparables to use, how to adjust for differences, and how to read current demand. Because it is not a certified valuation and often doubles as a listing pitch, two agents can reasonably arrive at different figures. Ask each to show the comparables and the reasoning behind the number.

Sources: Zillow and Redfin published accuracy disclosures, standard descriptions of the comparative market analysis and the licensed appraisal process, and 2026 cost figures for residential appraisals. Valuation accuracy varies by market and property; figures are general references, not guarantees.

This article is general information and analysis, not financial, lending, or appraisal advice. Verify any home value with a licensed professional before acting.