Kate H. asks: What is the value of 1988 penny mis-stamped. The coin itself is not the correct shape and is only stamped, front and back half way.
You have a cent struck on a clipped planchet, that is, an incomplete coin missing 10-25% of the metal. This results from an error in punching out blanks from metal strip. The punch accidentally strikes a portion of the strip already punched. They are described by collectors by their shape: curved, straight, ragged, incomplete and elliptical.
Years ago, these errors use to be difficult to find since the coins would get caught in counting machines and be retrieved and remelted. In the early 1980’s the Mint began weighing the coins instead of counting them resulting in large numbers of these errors finding their way into the stream of commerce. The value of these errors depends on the size and type of the clip (curved, straight, elliptical, partial, ragged). Some coins can even have multiple clips. Approximate value for the most common clips found on a 1988 cent: $1.