How Accurate Are Online House Valuations?

Online UK house valuations are typically accurate to within 5–15% of the eventual sale price — good enough for a rough figure, not good enough for a mortgage. Traditional automated valuation models (the postcode-average tools that most free portals use) are at the looser end; photo-aware AI valuations like Offrly aim to do better by reading each comparable's photos for condition the way a human analyst would and resolving prices at the street level.

Online house valuations vary widely — two reputable tools for the same UK home routinely disagree by £20,000 or more — and the difference usually comes down to what each model can actually see. Here are the four broad types, why they disagree, and what they cannot capture at all.

The broad types

Postcode-average tools

Free tools that look up the average sale price for similar properties in your postcode. Quick, easy, and useful as a rough ballpark, but blind to what any specific home actually looks like.

Comparable-based automated valuation models

Tools that look at recent sales of similar properties within a radius and adjust for beds, baths, property type and basic attributes. Better than a postcode average, but still blind to condition, garden, and the within-postcode quality variation that separates two homes on the same street.

Photo-aware AI valuations

Models that read listing photos to score condition and garden the way a human analyst would, combined with a hyperlocal regression that resolves prices to the street rather than the postcode. Offrly sits in this category.

Human professional

A RICS surveyor's physical inspection. The only option for a regulated figure that lenders and insurers accept.

Why online valuations disagree

Different tools will give you different numbers for the same property. This is normal. The reasons:

• Different comparable sets. One tool might use a 1-mile radius, another 2 miles.
• Different proxies for condition. Some assume average, others read photos.
• Different model architectures.
• Different freshness. Some update weekly, some on every query.

Running two or three tools and treating the rough middle as a starting point is a reasonable approach.

What online valuations miss

• Interior issues beyond what photos show, such as plumbing, wiring, boiler age.
• Structural issues.
• Damp, subsidence, Japanese knotweed.
• Lease length and ground rent for flats.
• Boundary disputes.
• Local flood risk.
• Upcoming planning applications nearby.

These are things a RICS survey catches. Online tools are a starting point, not a stopping point.

Where Offrly fits

Offrly is a free photo-aware AI valuation for the UK — a sharp first-pass price, free online. Our AI reads each comparable's photos the way a seasoned property analyst would, and a hyperlocal regression resolves prices down to the street rather than the postcode — capturing variation that traditional automated valuation models cannot. Thirty seconds from postcode to a point estimate with the comparables that fed it. No signup, no email.

Run a free Offrly valuation →

Disclaimer: An Offrly estimate is indicative market guidance, not a regulated valuation and not financial advice. For mortgage, insurance, probate or legal purposes, commission a RICS-qualified surveyor.