Methodology
How we value a slab
A slab's value comes only from completed sales of the same item at exactly the same grade. Here is precisely which sales count, how much each one weighs, and what happens when there are none.
The exact key
Every slab is keyed by its item and its full grade: grader, grade, label tier, qualifier, seal rating and packaging, plus the label type for graded games. Two slabs share a market only when every part of that key is the same.
- PSA 9 and PSA 10 are different markets.
- PSA 10 and CGC 10 are different markets. So are BGS 10 Pristine and BGS 10 Black Label.
- CGC Pristine 10 and CGC Gem Mint 10 are different markets, even though both say 10.
- A PSA 8 with a qualifier (for example PSA 8 OC) is not a PSA 8.
- WATA 9.4 A+ and WATA 9.4 A are different markets, and a sealed game is not the same as one complete in box.
Which sales count
Only completed sales count: the price someone actually paid. Listings and asking prices never enter a value. A sale must match the exact key with at least 85% certainty, and its source must allow us to use it for valuations.
The market value looks at the sales of the last 90 days. When that window holds fewer than 3 sales, it widens to 365 days. A market value never rests on a sale older than 365 days; without one, you get an estimate instead.
Newer sales weigh more. A sale's weight halves every 60 days when the window holds 3 to 5 sales, every 30 days with 6 or more, and every 120 days when the window had to widen. Every marketplace and auction house weighs the same. A sale someone typed in without a link to the listing would weigh 80% (adding your own sales isn't available yet).
The market value is the weighted median of the counted sales: sort them by price and take the one where half of the total weight is reached. With only one or two sales, it is the most recent one. Market values are rounded: from €1,000 to the nearest €10, below that to the nearest €1 (€41,798.89 becomes €41,800). The sales themselves keep their exact euro amount, so the audit adds up.
Currencies
Each sale is converted to euros at the ECB reference rate of the sale day and stored that way, with its original price shown next to it ($42,150 → €41,799). Values are never re-converted with today's rate, so exchange rates alone never move your chart.
Auction premiums
Auction houses add a buyer's premium to the hammer price. We count what the buyer paid, including the premium, so an auction sale and a fixed-price sale compare fairly. The audit says so on every auction row (for example “incl. 20% buyer's premium”). Shipping and taxes are never part of the price.
Not counted
Sales that don't belong in a value stay visible in the audit, marked Not counted, with one of these reasons:
- Best Offer · final price unknown
- Price uncertain · not the final price
- Uncertain title match · not verified
- Source not licensed for valuations
- Lot · several items
- Damaged slab
- Outlier, too high
- Outlier, too low
- Implausible next to the adjacent grade
- Outside the time window
Outliers are found with a robust test against the median of the other sales, so one extreme price can't drag a value. They are flagged, never deleted.
Estimates
When an exact grade has no counted sale in the past year, Slabfolio shows an estimate, and it always looks like one: an ≈ in front of the amount, a range, a confidence meter and the method in words (“From CGC Gem Mint 10 × 1.56”). Estimates are rounded more coarsely than market values: from €10,000 to the nearest €1,000, below that to the nearest €10.
We try several methods and keep the one with the highest confidence. Each method has a ceiling, because some are more reliable than others:
| Method | Highest possible confidence |
|---|---|
| Equivalent grader | 85% |
| Between two grades | 70% |
| Grade ratio | 65% |
| Last sale carried forward | 45% |
| Qualifier | 40% |
| Other grader | 35% |
| Raw price | 20% |
Confidence is high from 75%, medium from 50% and low below. Your own estimated slabs count toward your total, marked as estimates in the value basis. Estimates for grades you don't own, like a ladder rung, never count.
A worked example
Charizard, Base Set 1st Edition, PSA 9. These are sample sales from our demo dataset, not real market prices, so you can follow every step. Four sales in 90 days count. The newest weighs most; the median by weight is the eBay sale of Oct 7, 2026 at €41,799, which rounds to €41,800. The Best Offer without a final price stays visible, but it doesn't count.
Market value €41,800
Charizard · PSA 9 · exact · 4 sales/90d
| Date | Source | Price | Weight |
|---|---|---|---|
| Oct 7, 2026Median | eBayBuy It Now Cert-verified | €41,799$42,150 | 97% |
| Sep 21, 2026 | HeritageAuction incl. 20% buyer's premium · Cert-verified | €39,629$39,950 | 80% |
| Aug 30, 2026 | GoldinAuction incl. 20% buyer's premium · Title match | €43,651$44,000 | 62% |
| Aug 8, 2026 | eBayAuction Cert-verified | €39,854$40,300 | 48% |
| Jul 31, 2026 | eBayBest Offer | — | Not countedBest Offer · final price unknown |
Charizard · Base Set 1st Edition
Grade ladder · PSA
| Grade | Value | Note |
|---|---|---|
| PSA 10 | ≈ €248,000 | Estimate, confidence low, range €190,000–€310,000 |
| PSA 9 | €41,800 | Your slab |
| PSA 8 | €21,600 | 7 sales in 90 days |
| PSA 7 | €14,200 | 9 sales in 90 days |
| PSA 6 | €9,900 | 12 sales in 90 days |
Sample data: generated sales, not real market prices. The PSA 10 rung is an estimate: no PSA 10 sold in the past year, so its last sale is carried forward, and it doesn't count toward anyone's total.
What's sample data today
Slabfolio is in beta. The demo and the market pages run on generated sample data, as of Oct 10, 2026, and say so with a “Sample data” label on every value. Your own slabs never get sample values: until we connect a licensed source of graded sales, they show what you paid, marked At cost.
Where sales will come from
From licensed data providers that are allowed to give us completed sales, starting with graded Pokémon cards. We never scrape marketplaces. Every sale behind a value names its source.
What we never do
- Average across grades or across graders.
- Use listings or asking prices as sales.
- Hide a sale that didn't count. It stays in the audit with its reason.
- Sell your data, or let anyone pay for better values.
Values describe completed sales. They're not financial advice or an appraisal.