How StampWorth estimates value
The app turns one photo into an identification, a condition and rarity label, and an estimated value range. Here is how each step works, where it goes wrong, and which number to use when you sell, insure or divide a collection.
The value StampWorth shows is an AI estimate of a market-value range. It is not a lookup of sold prices, not a catalogue value and not an appraisal. Treat it as a first sort: what to research, what to protect, what to show an expert.
What happens when you scan a stamp?
- The photo is sent for identification. The app shrinks the photo and sends it to a general-purpose AI vision model run by OpenAI. The photo is used for that request only; your collection stays on your phone. The privacy policy has the details.
- The model identifies the stamp. It is told to work the way a philatelist would: confirm it is a postage stamp, read the country from text, symbols and currency, narrow the era from the design and printing, then match it to catalogue entries. It returns the issue, country, year, face value and a confidence score.
- It suggests catalogue numbers in Scott, Michel, Stanley Gibbons and Yvert & Tellier, where it can match them.
- It assesses condition from centering, perforations, gum and cancellation, and writes short condition notes.
- It estimates a value range, a low and a high figure in your own currency, and writes notes on what drives it. The model is instructed to be conservative with valuations.
The same steps run for each stamp when you scan a whole album page with Pro.
How sure is the identification?
Every result shows a confidence score. The model is asked to score an exact match at 90–100%, a strong match at 70–89%, a partial match at 50–69%, and anything lower as uncertain. Below 70%, treat the identification as a lead to check, not an answer. Many stamps exist in several near-identical printings that differ only in perforation gauge, watermark or shade, and a photo cannot always tell them apart. Those small differences can move the value a great deal.
What do the condition and rarity labels mean?
The app uses two short scales so results stay comparable across a collection. The wording below is the general sense of each label; the model assigns one from the photo and explains it in the condition notes.
| Condition label | General sense |
|---|---|
| Mint | Unused, as issued: full gum on an unused stamp, no visible faults. |
| Fine | Sound and attractive, with minor flaws such as slightly off-centre design or a light cancel. |
| Good | Clearly collectable but with visible wear: heavier cancel, poorer centering, small perforation faults. |
| Fair | Obvious faults that a buyer will price in. |
| Poor | Heavily damaged; usually space-filler value only. |
Rarity runs over six steps: common, uncommon, scarce, rare, very rare and extremely rare. Most stamps people find in an album are common.
Dealers and auction houses grade more finely than five steps, and price faults one by one. Our condition faults guide sets out what a thin, a tear, fading, damp or poor centering usually does to the price, and the grading guide explains the grades dealers use.
Where can the estimate be wrong?
- It is not built on sold prices. The estimate comes from the model’s general knowledge of stamps and their markets, not from a database of auction results or completed sales, so it can be out of date or off for a particular market.
- Catalogue numbers are suggestions. The app does not read from a licensed catalogue. Check the number in the catalogue itself before you quote it.
- One photo shows one side. Thins, creases, repairs and regumming are often on the back or only visible under light at an angle. A photo of the front can rate a damaged stamp too high.
- Forgeries, reprints and repairs. The app cannot authenticate a stamp. The rarer and more valuable a stamp looks, the more likely it is to be a forgery or reprint, and the more an expert certificate matters.
- Varieties and errors. A missing colour, an inverted centre or a rare perforation can be invisible at phone resolution, so a valuable variety can be valued as the ordinary stamp.
- Collections are not sums. A running total of single-stamp estimates is not what a dealer will pay for the lot. Bulk material sells for a fraction of the sum of its parts.
If an identification looks wrong, use “Report a problem with this result” in the app, or email support@ichime.dev.
Which number do you need?
The same stamp has different values depending on why you are asking. The app’s range is a starting point for each, never the final figure.
| Purpose | The number that counts | Where to get it |
|---|---|---|
| Selling | What a buyer pays today, after fees | Sold prices for the same stamp in the same condition; dealer or auction offers. See selling stamps. |
| Insuring | What it would cost to replace | A written valuation if your insurer wants one. See insurance value. |
| An estate or inheritance | Fair market value at the relevant date | A qualified appraiser, documented. See estate valuation and inherited collections. |
| Keeping and sorting | Roughly which stamps matter | The app’s estimate is usually enough to decide what to protect and what to research. |
What sources should you check the estimate against?
- Sold prices, not asking prices: auction prices realised and completed marketplace sales for the same stamp in the same condition. The eBay listings Pro shows in the app are current asking prices, useful for a feel of the market but not proof of value.
- The catalogue your buyer uses: Scott in the US, Stanley Gibbons in the UK, Michel in Germany, Yvert & Tellier in France. Catalogue value is a reference for top-grade retail, and most stamps sell well below it.
- An expertising body or certified appraiser for anything valuable, before you sell, insure or divide it. A certificate from a recognised expert is what buyers of expensive stamps expect.
How the guides on this site are written
The guides are drafted with an AI writing model and checked automatically before publishing. A draft is rejected if it states a price, print run, auction result or the name of an expert or auction house that is not on a short list of checked facts, if it links outside this site, or if it repeats an existing guide. The hub pages, home pages and this page are written and edited directly. There is no named expert author or reviewer; the byline is “StampWorth editorial”. More on the about page.
See the estimate for your stamp
StampWorth identifies the stamp from a photo, grades its condition, suggests its catalogue numbers and gives an AI estimate of its market-value range — a starting point, not a sale price. Free to download on iPhone and Android: 3 identifications a day, and your first valuation shows its full value; Pro shows every value.