Why Offrly publishes accuracy in the open
Almost no free UK valuation tool publishes a real accuracy figure. The ones that do tend to cite proprietary back-tests no one can verify. Offrly's stance is the opposite — every published valuation is logged, paired against the eventual HM Land Registry sold price for the same property, and fed into a public accuracy report. The figures aren't a marketing claim; they're a curated prediction-vs-outcome record you can read.
- Public accuracy report at /accuracy-report.
- Every figure traces to a real Offrly prediction and a real HM Land Registry sold price.
- Predictions are made strictly before the eventual sold date — no leakage.
- Only admin-confirmed pairs feed the published metrics.
- Rentals are not in the report — there's no public sold-rent register to pair against.
The problem with "free valuation" accuracy
Most free UK valuation tools either:
- Don't publish an accuracy figure at all, or
- Cite a proprietary back-test ("our model is 93% accurate") that no third party can audit.
The second is worse than the first. A back-test on the model's own training period inflates the result. A back-test on data the model has already seen tells you nothing about how it performs on next month's homes. And a self-reported number with no auditable source can be set to whatever marketing wants.
What Offrly does instead
Every Offrly sale valuation is logged with its postcode, predicted price and timestamp. When HM Land Registry publishes its monthly sold-price drop, candidate pairings surface — full postcode match, sold date after the valuation date — and an admin confirms the right one using the available context. Only confirmed pairs feed the public report at /accuracy-report.
The figures published:
- Hit rate within ±10% — the share of Offrly estimates that landed within 10% of the actual sold price.
- Hit rate within ±20%.
- Median absolute percentage error (MdAPE).
- Mean absolute error in £ (MAE).
- Per-property-type breakdowns (detached, semi-detached, terraced, flat).
Each figure traces to a real Offrly prediction made strictly before the eventual sold date. By construction, predictions never see future sold prices.
Why HM Land Registry?
HM Land Registry Price Paid Data is the authoritative record of every residential property transaction in England and Wales, published monthly under the Open Government Licence. It's the only licence-free primary-source sold-price dataset for those nations. Using it as the ground-truth means the accuracy claim is auditable by anyone with an internet connection.
Scotland uses Registers of Scotland; Northern Ireland uses Land & Property Services. Those datasets aren't yet integrated into the accuracy report — the curated pair set is England-and-Wales for now.
What's NOT in the accuracy report
- Rentals. No public sold-rent register exists, so we don't publish a rental accuracy claim.
- Probate, mortgage and insurance valuations. Those are regulated processes; Offrly's estimate is indicative market guidance, not a binding figure. The accuracy report measures market-pricing accuracy, not regulated-valuation equivalence.
- Off-market or pocket-listed sales. HMLR captures completed transactions only; off-market chats don't show up.
And the practical implication
If you're choosing between Offrly and another free tool: read the accuracy report. If the other tool publishes one against an authoritative sold-price register, compare them honestly. If it doesn't, that's a meaningful signal in itself.
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How is the accuracy figure computed?
Every Offrly sale valuation is logged with its postcode, predicted price and timestamp. When HM Land Registry publishes its monthly sold-price update, candidate matches surface where a logged valuation's full postcode shows up with a sold date after the valuation was made. An Offrly admin reviews each candidate against available context — full address (when supplied via a public listing URL), property type, sold-price plausibility — and confirms the right pairing. Only confirmed pairs feed the published metrics.
Why curated rather than automatic?
A full UK postcode unit holds 10–15 properties, so postcode + sold date alone can match 0, 1 or several HMLR rows to a single valuation. The model can't always disambiguate, especially when the user didn't supply a listing URL. A human admin closes the loop using the available context. Every curated pair is auditable and reversible.
Can the headline figure get worse?
Yes. As more pairs are curated, the headline figure can move in either direction. We commit to publishing the current curated set; we don't cherry-pick to keep the number flattering. The page recomputes on every load.
What about rentals?
Rentals are NOT in the accuracy report. There is no public sold-rent register equivalent for rentals — HM Land Registry covers sale prices only, in England and Wales. Publishing a rental accuracy claim without a public ground-truth would be a marketing claim, not an accuracy claim, so we don't.
Are there any internal accuracy claims Offrly makes that aren't published?
No. The figures on /accuracy-report are the only public accuracy claim Offrly makes. We don't cite model internals, proprietary benchmarks or cherry-picked cases.