Are error coins worth money?

The short answer

A few are worth a great deal and most are worth very little, and the difference is whether the fault happened inside the mint or afterwards. Damage in a pocket, a machine or a vice is not an error, and it is the explanation for the overwhelming majority of unusual-looking coins people find.

Mint error or later damage

A mint error happened while the coin was being made — a blank of the wrong metal, a strike off centre, a die that cracked, two coins struck together. Post-mint damage happened after it left, and it covers almost everything that arrives in an envelope marked "rare error": coins run over, acid-etched, spooned, hammered or spun in a machine.

The distinction is settled by asking what the press could have done. A press cannot add metal, polish one side, or bend a coin without flattening its design; it can only strike a blank wrongly, or strike the wrong blank. Anything that could not have come out of a press came from somewhere else.

Errors that carry real money

A coin struck on the wrong blank, which is checked with a scale rather than the eye and is the reason weight is the first test on any suspected error. A strike far enough off centre that part of the design is missing, priced by how much is missing and by whether the date survived. A doubled die, where the doubling was cut into the die itself and so appears identically on every coin struck from it.

What they have in common is that each is verifiable against a published specification or a documented variety. An error nobody has documented is a coin with an unusual appearance and no market, however unusual it looks.

The doubling mistake

Most coins that look doubled show machine doubling, which happens when the die shifts slightly as it lifts and smears the design sideways. It is flat, shelf-like and duller than the surrounding metal, it is common, and it adds nothing to the value.

A true doubled die shows a second image with its own rounded relief and its own clear edges, and it appears in the same place on every coin from that die pair, which is why the genuine ones are catalogued by series and year. If the doubling is shiny and flat, it is machine doubling, and the answer is no.

If you think yours is genuine

Weigh it, measure it, and compare it against the specifications for that issue in the coin value catalogue before going any further, because a wrong-metal error is proved by the scale and nothing else. Then check whether the variety is documented for that series and year, rather than searching for a coin that looks like yours.

Errors that survive those two steps are worth authenticating, for the reason in should I get my coin graded: an error is only worth what a buyer can be convinced of, and on errors the convincing is what the holder is for.