Accuracy
How wrong we have been
Every figure we publish, scored against what the property sold for.
Median error
Within 10%
Bias
Calibration gap
Not published yet. A property has to sell before we can be marked on it, and we hold figures back below 20 completed sales. 5 valuations published, 0 matched to a sale so far.
Why this page exists
Every other quality signal is us marking our own homework.
A confidence score is a claim. The only thing that settles it is a figure we published, compared with what the property really sold for. So we store every valuation and score it when HM Land Registry catches up.
Research puts UK automated valuation models within 10% of the sale price about 70 to 80% of the time. No consumer portal publishes the realised error of its own estimates, which is why the industry figure is the only one anyone can quote.
- Median error
- Half our valuations are closer than this.
- Within 10%
- Share landing within a tenth of the sale price.
- Bias
- Positive means we run high. Zero is the target.
- Calibration gap
- Realised within-10% rate minus the odds we claimed. Negative means we were overconfident.
Method
Only later sales count
A sale must be at least 14 days after we valued. A same-week sale was already agreed, so scoring it would flatter us.
Market drift is not our error
The estimate is indexed forward to the month of the sale before the two are compared, so a rising market is not counted as accuracy.
Forced sales excluded
HM Land Registry Category B sales, which include repossessions, are left out. A correct valuation should not be punished by a distressed price.
Nothing below 20 sales
A median over four sales is a number, not a measurement. Below the floor we publish the count and no metrics.
Blend 2026-08-31.asking-pillar. Measured 2 September 2026.
Asked most
How accurate are online property valuations in the UK?
Research on UK automated valuation models puts them within 10% of the eventual sale price roughly 70 to 80% of the time, so about one in five estimates is more than 10% out. No consumer portal publishes the realised error of its own estimates, so those figures are industry-wide rather than specific to any one tool.
Does PropM8 publish its own valuation accuracy?
Yes. Every valuation we publish is stored, and when HM Land Registry later records the property selling, the two are compared. This page reports the median error, the share landing within 10% and 20%, the signed bias, and the gap between the confidence we claimed and the accuracy we achieved.
Why can a valuation be wrong even with good data?
Public data cannot see condition, layout, aspect or a recent refurbishment. An extension or a new kitchen can move value by a tenth or more and appears in no register until the property sells. PropM8 handles this by publishing a range with a stated confidence rather than a single figure, and by letting you correct the facts it could not read.
What is a calibration gap in a property valuation?
A calibration gap compares the confidence a valuation claims against the accuracy it actually delivers. If a tool says a figure has a 60% chance of landing within 10% and it lands within 10% only 45% of the time, it is overconfident by 15 points. It is the check that stops a confidence score from being decoration.