Methodology

How 996Value.com values a 996

Every number on this site follows the rules on this page. If a figure ever conflicts with them, the rules win and the figure gets fixed.

The dataset

543 verified auction sales of 1999–2005 Porsche 911 (996) cars, collected from the auction listings themselves, never estimated. Sources: Bring a Trailer, Cars & Bids, PCarMarket, Collecting Cars, and Hemmings. The dataset grows with weekly sweeps of new results. The whole dataset is public in the sales index, every sale linked back to its original listing.

Hammer-price basis

All sold figures are hammer prices: the winning bid, excluding buyer fees, so numbers reflect what the car sold for rather than the all-in transaction. Where a venue displays prices that already include a premium and the premium percentage cannot be verified from a primary source, those sales are held out of the dataset rather than guessed — the rule is: a price we cannot state exactly does not ship. Non-US prices are converted at the Bank of England daily spot rate for the sale date, with the rate recorded on the sale.

How valuations are computed

• The headline estimate comes from a hedonic regression fitted to 494 verified stock sales, 2017–2026 (modified cars — engine swaps, forced-induction builds, safari conversions, per the listing notes — are excluded; a stock engine replacement is not a modification). Terms: variant, continuous mileage, transmission, body, documented IMS work, auction venue, and sale month.
• Estimates are priced at the current month and venue-neutral: the venue terms are blended at the dataset's venue mix rather than pricing your car as a listing on any one site.
• The range shown is an 80% prediction interval from the regression — where most comparable cars land — not the min–max of past sales.
• The previous band lookup (variant × mileage band medians, 2021 onward) still runs as a check on every result. A disagreement over 20% is flagged, with the band's comps shown.
• Transmission and body are inside the model now: the 6-speed manual measures +22.4% and the cabriolet −11.9% against their counterparts, holding the rest constant.
• On a time-based holdout (fit on sales before October 2025, tested on the year after), the model's median error was 12.7%, against 15.7% for the band lookup — and the model prices every variant, where the bands had no answer for 15% of recent sales.

Measured adjustments (modifiers)

Adjustments are estimated by regression on the verified dataset and refreshed as the dataset grows. Only adjustments the data supports are applied in the calculator; the rest are tracked in the open.

Two more effects the regression measured: comparable cars bring about 15% less on Cars & Bids than on Bring a Trailer with variant, mileage and timing held constant — the raw gap is about 38%, but most of it is the mix of cars each venue sells (Cars & Bids' median car has 76,100 miles; BaT's has 44,000) — and prices drift about +3.3% a year across 2017–2026. The calculator's headline estimate blends the venues rather than pricing your car as a BaT listing.

Asking prices

Asking prices live in a separate dataset (snapshots of PCA Mart and Rennlist listings, captured weekly) and are never blended into sold-price medians — asks run systematically above hammer prices. The ask-to-hammer spread is measured only on cars matched by VIN between the two datasets: same car, its asking record, then its auction result. Until enough matched pairs accumulate, the site shows the two figures side by side, labeled, and blends nothing.

Changelog

• October 19, 2026 — Multi-source dataset unified on one banded basis (2021+, stock, mileage-documented) across the calculator, model pages, and articles; modifier adjustments added to the calculator (IMS first).
• October 18, 2026 — Cars & Bids harvest completed and merged; dataset passed 500 verified sales.
• October 2026 — Asking-price dataset started (PCA Mart and Rennlist snapshots, VIN-keyed).