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 frozen at quarter-end and matched to the HM Land Registry sale of the same home, then fed into a public accuracy report. The figures aren't a marketing claim; they're a record of estimate against sold price you can read, with no human in the loop.
- Public accuracy report at /accuracy-report.
- Every figure pairs a real Offrly prediction with the HM Land Registry sale of the same home — never a neighbour's sale.
- A valuation never looks up the Land Registry record of the home being valued, so its sold price can't leak into the estimate.
- Pairing is fully automated — no admin chooses which pairs make the cut.
- 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, house number or name (where you gave one), predicted price and timestamp. At quarter-end the BUY rows are frozen to an immutable snapshot, and each is matched to the HM Land Registry sale of the same home — the same full postcode and the same house number or name, never a neighbour's sale on that postcode. Each home is paired with its open-market sale closest in time to the valuation, before or after it, within two years. There is no human in the loop. The lifetime aggregate is published at /accuracy-report; the per-quarter sealed snapshot is at /benchmark.
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), once each type has enough matched homes to report honestly.
A valuation never looks up the Land Registry record of the home being valued, so a sale that had already completed can't leak into its estimate — and the report says how many of the matched homes sold after the valuation and how many before.
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 matched 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 valuation 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.
How is the accuracy figure computed?
Every BUY valuation Offrly issues in a given quarter is frozen to an immutable snapshot at quarter-end. Each frozen valuation is matched to the HM Land Registry record of the same home — the same full postcode and house number or name — and paired with that home's open-market sale closest in time to the valuation, before or after it, within two years. The metrics on /accuracy-report aggregate every quarterly snapshot; /benchmark shows a single quarter at a time.
Why match the exact home rather than the postcode?
A full UK postcode holds 10–15 properties, often of different types and sizes. Pairing a valuation with any sale on its postcode mostly measures the neighbours — a four-bed detached against a one-bed flat across the road — and picking the closest-priced of several sales flatters the model. So only the sale of the home that was valued counts: same postcode, same house number or name. If that home sold more than once in the window, the sale closest in time wins, never the one closest in price.
Why do sales from before the valuation count?
Because a valuation never looks up the Land Registry record of the home being valued, so a sale that had already completed can't leak into its estimate. Counting only sales after the valuation would leave the report nearly empty, because few homes sell within a year of being valued. The report says how many matched homes sold after the valuation and how many before, and the two-year limit stops market movement passing for model error.
Can the headline figure get worse?
Yes. As fresh HMLR data lands and new quarterly snapshots resolve, the headline figure can move in either direction. We don't cherry-pick to keep the number flattering — the report recomputes over every snapshot whenever new data lands.
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 and /benchmark are the only public accuracy claims Offrly makes. We don't cite model internals, proprietary benchmarks or cherry-picked cases.
Run both. Ours prices the home, not the postcode.