Offrly Sealed Benchmark — 2026Q3
Auto-generated, immutable. Snapshots can't be re-curated, re-cherry-picked or re-tuned after the fact — the figures move only as HM Land Registry publishes new sales of the homes in them.
How the benchmark works
- Snapshot. At the end of each calendar quarter, every BUY valuation issued in that quarter is frozen to
data/benchmark/<quarter>.jsonl. The snapshot file is not rewritten. - One valuation per home. Within the quarter's snapshot we collapse to the latest BUY valuation per home — the same full postcode and house number or name. If a home was valued more than once, only the most recent prediction is scored, so no home inflates the sample.
- Match the same home. Each valuation is matched to that home's own HM Land Registry record — the same postcode and the same house number or name (for a flat, the flat number). A sale of another home on the same postcode never counts, and valuations without a house number aren't scored. No admin reviews these matches.
- Pair one sale. Each home contributes only its latest BUY valuation, matched on full postcode and house number or name, and is paired with the open-market HM Land Registry sale of that same home closest in time to the valuation (before or after it, within 24 months) — never a neighbour's sale on the same postcode. A valuation whose property type doesn't match the Land Registry record is left out: it described a different home. In this quarter, 0 matched homes sold after the valuation and 14 before it.
- Metrics. Compute hit rate ±10/±20%, MdAPE, MAE, and confidence-band coverage — the share of sold prices that landed inside the band displayed at valuation time (a 90% interval since July 2026; 95% before). Publish all of them — even when they're unflattering.
What's in the report, transparently
- Scope: sale valuations only. Rentals are not included — there's no public sold-rent equivalent.
- Ground truth: HM Land Registry Price Paid Data — every arms-length freehold and most leasehold residential sales in England and Wales.
- Licence: Open Government Licence v3.0.
- Curation: none. Every BUY valuation issued in the snapshot quarter is in the benchmark population.
- Leakage controls: an Offrly 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. A sale after the valuation is a true forecast; the pairing step above says how many of each this quarter holds.
- Update cadence: a new snapshot freezes when each quarter closes, and matches are added as HM Land Registry publishes each month's sales.
For more context on how Offrly produces a price in the first place, see how Offrly works.
Frequently asked questions
How is the benchmark different from the accuracy report?
Both pages run on the same matching — every BUY valuation is frozen at quarter-end and scored against the HM Land Registry sale of the same home. The benchmark shows a single quarter's snapshot, sealed and dated. The accuracy report aggregates every snapshot into a lifetime view so the sample is larger. Neither has a human in the loop.
What does 'band coverage' mean?
Each Offrly valuation shows a likely range alongside the estimate — a 90% interval since July 2026, 95% before. Band coverage is the share of real HMLR sale prices that fell inside the range shown at the time: the test of whether the claimed range matches reality. A well-calibrated 90% range covers about 90% of outcomes.
What if the same home sold more than once?
We take its open-market sale closest in time to the valuation — never the one closest in price, which would flatter the model. Sales of other homes on the same postcode never count, however close their price.
Are snapshots really immutable?
Yes. Once written, the snapshot file is not rewritten. New HMLR sales arriving later can add matches, but they cannot change which valuations are in the snapshot — those were frozen when the quarter closed.
Source: HM Land Registry Price Paid Data, licensed under Open Government Licence v3.0. Offrly estimates are indicative market guidance — not regulated valuations and not financial, tax or legal advice.