Broker price opinion, appraisal or online estimate: what is the difference?

The difference is who produces the number, what they looked at, and who is answerable for it.

An online estimate comes from an automated valuation model working from records. A broker price opinion, or BPO, comes from a real estate professional. An appraisal comes from a licensed or certified appraiser who follows professional standards and supports the conclusion in a written report.

A real estate broker, agent or salesperson prepares it, and it estimates the probable selling price.

That wording comes from federal law, which defines a broker price opinion as an estimate by a real estate broker, agent or sales person that details the probable selling price of a particular property. The agent may drive past, walk through, or work from listings, depending on what was requested. It reflects market knowledge, which is valuable, but it is not produced under appraisal standards.

Not as the main basis for the value on a purchase loan for a principal home.

Federal law says that in connection with the purchase of a consumer's principal dwelling, a BPO may not be used as the primary basis to determine the property's value for originating a residential mortgage loan. Separately, the Interagency Appraisal and Evaluation Guidelines say valuation methods that do not provide a property's market value, such as a broker price opinion, are not acceptable as an evaluation.

At the bottom for any decision that someone else has to rely on.

It is free and instant, and it is fine for curiosity. But no person has looked at the home and nobody signs it. The same interagency guidelines say a tool such as an AVM cannot be substituted for an appraisal when a transaction requires an appraisal.

That depends on who is going to rely on the number.

If you are just curious, an online estimate costs nothing. If you are talking about a listing price, an agent's opinion reflects what buyers are doing right now. If a lender, a court, an estate or another party will lean on the value, ask them what they accept. Often the answer is an appraisal. Pocket Appraisal is a national residential appraisal service for owners who want to get an actual appraisal rather than an estimate.