How does Zillow actually calculate a Zestimate?
Zillow's own description is a proprietary model built from public records, tax assessments, prior sale prices, and, where licensed, MLS data, plus any facts a homeowner has submitted directly. For a home currently listed for sale, the model can also see the listing price, description, and days on market. For a home not currently listed, it works entirely from public record and comparable-sale data, which is a meaningfully different, and less current, set of inputs.
How far off can a Zestimate actually be in dollars?
Zillow's published figures put the nationwide median error at 1.83% for on-market homes and 7.01% for off-market homes. Applied to New Hampshire's July 2026 statewide median sale price of $580,000, that 7.01% off-market margin works out to roughly $40,660 in either direction, before you even get into whether your specific house is typical for its area. On a $900,000 home, the same percentage is over $63,000.
Why is my off-market Zestimate less accurate than an on-market one?
An off-market Zestimate can't see your asking price or your home's actual current condition, so it leans harder on assessed value and whatever comparable sales exist nearby. In a market moving as fast as New Hampshire's has in 2026, comparable sales from even six months ago can already be stale.
Does a Zestimate know about my renovation or a problem with the property?
Only if it's been recorded. The model has no way to know about a finished basement, a new kitchen, or a failing well that hasn't been reflected in a permit filing, an assessment update, or a homeowner-submitted fact on Zillow's own site. It also can't account for a neighboring "comparable" sale that was actually a fixer-upper, or one that was priced unusually for reasons specific to that seller.
What actually gets closer to a home's real value than an automated estimate?
A comparative market analysis built from genuinely comparable closed sales, adjusted for condition, lot, updates, and location, and walked through in person rather than pulled from a database. That's not the same thing as an appraisal, which is a formal, licensed valuation with its own separate standards, but it's a closer read than any automated model working from public records alone.
If you're deciding whether to trust your Zestimate before pricing a sale, the fastest way to check it is against actual comparable sales in your specific neighborhood.
