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Offrly Sealed Quarterly Benchmark

Auto-generated, immutable. Snapshots can't be re-curated, re-cherry-picked or re-tuned after the fact — this report is what it is the moment HMLR publishes the matching sales.

Benchmark pending. The first sealed snapshot is taken at quarter-end, then we wait six months for HMLR to publish the matching sales. Until that pairing arrives, this page is live for crawlers but does not show synthetic numbers. The methodology below describes the pipeline in full.

How the benchmark works

  1. 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.
  2. Wait. HM Land Registry publishes its sold-price data with a delay; we let six months pass so most matched sales are available.
  3. One valuation per postcode. Within the quarter's snapshot we collapse to the latest BUY valuation per full postcode. If the same property was valued more than once, only the most recent prediction is scored — so a postcode never inflates the sample.
  4. Auto-join. For each surviving valuation we look up sales on the same full postcode that completed after the valuation date. No admin reviews these matches.
  5. Tie-break. When one postcode has multiple HMLR sales after the valuation date, pick the sale whose price is closest to the prediction.
  6. Metrics. Compute hit rate ±10/±20%, MdAPE, MAE, and 95%-band coverage. Publish all four — even when they're unflattering.
What this number means, and what it doesn't. The benchmark is an unfalsifiable public read on Offrly because we deliberately do not curate which pairs feed it. The trade-off is that the postcode tie-break (closest-by-price) biases each individual pair toward the model. We surface that explicitly rather than hiding it. For the lifetime aggregate of every quarterly snapshot, see the accuracy report — same auto-join, larger pooled sample.

What's in the report, transparently

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 auto-join — every BUY valuation is frozen at quarter-end and matched to HMLR sales on the same postcode six months later. 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 '95%-band coverage' mean?

Each Offrly valuation has an internal 95% prediction band. Band coverage is the fraction of true HMLR sale prices that fell inside that band — the calibration test of whether the claimed range matches reality. A well-calibrated 95% band covers ~95% of outcomes.

What happens when one postcode has multiple sales?

We pick the candidate sale whose price is closest to the prediction. This is the most charitable read for the model and we surface that explicitly so reviewers know — there's no hidden choice.

Are snapshots really immutable?

Yes. Once written, the snapshot file is not rewritten. New HMLR sales arriving later add candidates to the auto-join but they cannot change which valuations are in the snapshot — those were frozen at quarter-end.

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.