How homes are actually valued
The dominant method for residential property is the sales comparison approach: appraisers and agents look at recently sold homes ("comps") that are similar in size, condition, age, and location, then adjust for differences. A comp with an extra bathroom or a renovated kitchen is adjusted downward to match the subject home, and so on. Recent, nearby, similar sales carry the most weight because they best reflect current market conditions.
Online estimates and calculators rely on the same logic applied to public data, which is why they are useful for a ballpark but imperfect for any specific home. They cannot see a gut renovation, a new roof, deferred maintenance, or a premium view. Treat any automated estimate as a starting range, not a precise figure, and narrow it with knowledge of the individual property.
When you need a real appraisal
For high-stakes decisions, a licensed appraisal is worth the few hundred dollars it costs. Lenders require one before approving a purchase or refinance, and it is the figure that governs how large a loan you can get. An appraisal is also the cleanest way to remove PMI once you believe you have crossed 20% equity, or to price a home confidently before listing it.
Remember that value and price are not the same thing. Appraised value reflects defensible comparable sales, but the price a buyer will actually pay depends on demand, competition, and emotion. In a hot market homes routinely sell above appraised value; in a slow one they sit below it. Use an estimate to set expectations, then let the live market confirm the real number.