An automated property valuation provides an estimated sale price. But the estimate alone does not tell you how much uncertainty surrounds it.
Forecast Standard Deviation, or FSD, helps explain that uncertainty. It gives users of an Automated Valuation Model (AVM) a way to assess the confidence behind an estimate, rather than treating every valuation as equally dependable.
What does FSD mean?
FSD measures the expected spread of sale prices around an estimated value, usually expressed as a percentage.
A lower FSD indicates less uncertainty and greater confidence in the valuation. A higher FSD indicates a wider spread of possible outcomes.
As a rule of thumb, an FSD of 8% means roughly two-thirds of sale prices are expected to fall within 8% of their estimates. This is an approximate statistical interpretation, not a guarantee for an individual property.
It also does not mean the valuation is “92% accurate”. FSD describes uncertainty around an estimate, rather than assigning it a percentage score for correctness.
Why do some valuations have a higher FSD?
Some properties are easier to value than others.
A home with a recent recorded sale and several similar properties sold nearby may have strong supporting evidence. An unusual property, or one in an area with few comparable transactions, can be harder to assess.
The age and relevance of sales evidence, differences between comparable homes and the information available about the property can all affect valuation uncertainty. How these factors influence FSD depends on the provider’s methodology.
A higher FSD does not necessarily mean an estimate is wrong. It signals that there is more uncertainty around it.
How is FSD different from a confidence rating?
A confidence rating such as High, Medium or Low provides a quick overview. FSD adds numerical detail.
Two valuations can sit within the same confidence category while having different FSDs. Seeing the underlying figures helps users distinguish between them without relying solely on a broad label.
Confidence categories and their thresholds can vary between providers, so it is worth checking how each service defines them.
Is FSD the same as a valuation range?
FSD and valuation ranges both communicate uncertainty, but they are not interchangeable.
A valuation range gives a lower and upper price estimate. FSD expresses uncertainty as a proportion of the estimated value.
To interpret a published range correctly, users should check the provider’s explanation of how it is calculated and what proportion of sale prices it is intended to capture. An FSD percentage should not automatically be treated as the full valuation range.
How can FSD support property decisions?
FSD can help teams compare the uncertainty of estimates across a portfolio and identify properties that need closer review.
For example, a team might use FSD alongside other checks to decide which valuations need additional comparable evidence or a professional assessment. The appropriate level of uncertainty will depend on the purpose of the valuation and the consequences of getting it wrong.
FSD should therefore support judgement, not replace it. A low figure is not a guarantee, and a higher figure is a reason to investigate rather than automatically dismiss an estimate.
Looking beyond the headline value
A useful valuation should communicate both an estimated price and the uncertainty around it. FSD helps users understand that distinction and make more informed use of automated estimates.
Chimnie offers FSD alongside its rated property sale valuations, giving customers a clearer view of the confidence behind each estimate.
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