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You can always guess. But if you need to get a firm grip on home value – either because you are considering selling or because you need to update your property’s insurance policy – here are three great home price estimation tools:

Multiple listing services

Local real estate groups manage databases of home sale prices and other details. These databases are known as multiple listing services (MLS). The list of comparable sales an agent shows you in her “free market estimate” comes from the MLS. All those house listings you see on Zillow, Trulia and They’re all pulled from MLS data.

You can access MLS information about completed sales without asking an agent to spend time and effort preparing an estimate for you. Many newspapers run weekly listings of recent home sales, typically in an agreement with the local MLS. Find out when the data is published (usually on the weekend) and scan for houses near you to build a neighborhood database.

Advantages: MLS data flows fast and furious. You are likely to find the latest home sale prices and price estimates.

Disadvantages: The data is incomplete and not always accurate. First, not every house sells through the MLS. About 10% of houses sell  “by owner” or from one investor to another, according to the National Association of Realtors. These sales bypass the MLS, but it is important to include them when you are collecting sales of houses comparable to yours.

Recently reported academic research also found that in 8.75% of MLS listings, the home prices were inaccurately reported, usually reflecting sales prices higher than they actually were.

Federal Housing Finance Agency (FHFA)

Another great source of house price trend data is available monthly through the Federal Housing Finance Agency. The data offered is based on mortgages refinanced through Fannie Mae and Freddie Mac, which buy mortgages from lenders to keep cash flowing through the home lending system.

For instance, FHFA data recently reported that house prices rose nationally from May 2015 to May 2016 by 5.6%.

You can use the House Price Calculator to apply the trend data to your house.

Advantages: FHFA data shows where markets are heating up and cooling down, giving you additional context for a real estate estimate.

Disadvantages: The data illustrates theoretical home value and can be a starting point to see how local trends might shape the value of your house. But it’s an informed guess. The data tend to lag behind the market and won’t reflect fast-moving local conditions.

Data estimators

With all of this data available, some companies create automated value estimators. When you use these, look for an explanation of the methodology it deploys. You want to see that the calculator allows you to add variables, such as improvements you have made to your house.

For example, Freddie Mac has an estimator for appraisers that blends the latest mortgage-based home sales data with changes in home value based on improvements. It’s one thing if a house increases in value along with all the other houses on the block. It’s another if the house increases in value because its owners added a family room. “Hedonic” models include changes like that.

Advantages: Sophisticated home value estimate tools let you see how much value might be added by different types of improvements. You can also build and save a model to create a snapshot of home value for your files.

Disadvantages: When you plug data into the calculator, it probably captures that information and adds it to an underlying database. You might be unwittingly inviting inquiries from real estate agents or signing up for mailing lists.

The most reliable source of market value is always a home appraisal. An appraiser is a professional who comes to your house to look it over, review detailed records of home value for your area, and then hand-calculate estimated value. It should also be noted that mortgage lenders only accept appraisals as part of the mortgage approval process. Find qualified appraisers through your state’s licensing agency website, and expect to pay about $300 for the appraisal.

Insurance terms, definitions and explanations are intended for informational purposes only and do not in any way replace or modify the definitions and information contained in individual insurance contracts, policies or declaration pages, which are controlling. Such terms and availability may vary by state and exclusions may apply.