Online property estimates can be a convenient starting point, but they do not answer every valuation question. An automated model works from the data and assumptions available to it. A professional valuation combines market evidence with an inspection, property-specific enquiries and judgement for an agreed purpose and date.
A difference between the figures does not automatically prove that either process has malfunctioned. It usually means the inputs, date, property knowledge or purpose differ. The appropriate figure depends on the decision for which it is required.
What an automated estimate may know
Automated estimates may draw on registered transactions, broad property attributes and market trends. These sources can cover large areas consistently, but public sales data arrives after registration and may not be complete for the newest transactions. Basic records may also describe a home less precisely than an inspection does.
A model may not know the current internal condition, exact floor area, quality of alterations, outlook, noise, lease clauses or whether two apparently similar flats occupy very different positions in a building.
What the valuer adds
The valuer agrees the interest, purpose, users and valuation date, inspects to the agreed scope and evaluates evidence that is relevant to that specific instruction. They can investigate why one comparable achieved a different result and judge whether it deserves weight.
Professional judgement is not a licence to ignore data. RICS expects adequate due diligence, reasonable verification and records supporting the conclusion.
Common causes of a difference
Differences often arise because an estimate uses a broad trend or assumed attributes while the valuer considers facts visible at the property. The valuation may also relate to a past date, an unusual legal interest or a scheme-specific assumption that an ordinary consumer estimate was never designed to address.
- Recent extension, conversion or deterioration
- Short lease, ground rent or shared ownership interest
- Exceptional outlook, floor level, garden or parking
- Scarce genuinely similar completed sales
- Different valuation dates or property assumptions
How to query a professional valuation
Ask the valuer to explain the evidence and assumptions rather than presenting an online estimate as a substitute report. If you know of a completed comparable, provide its address, date, price and any information about its condition or tenure. The valuer can decide whether it changes the analysis.
A professional valuation remains an opinion, not a guaranteed sale price or acceptance by a third party. Use it only for its stated client, purpose and valuation date. If the property data supplied to an online service is wrong, correct that record separately rather than asking the valuer to mirror it.
Advice for your property
Get the right professional inspection
Online guidance is useful, but it cannot account for the construction, condition and history of an individual property. Tell us what you are buying or need valued and we will explain the appropriate service.
Authoritative sources and further reading
The guide is general information, not property-specific, structural, legal, tax or financial advice. Source pages can change; consult the relevant professional for your circumstances.