The amount of silver in old coins is the main factor in determining value. Once the silver content is known based on weight, the coin can then be valued based on the current market value of silver, which fluctuates daily based on the market.
The amount of silver in coins determines the minimum value based on if the coin was melted down for the silver content. Other factors such at the year, rarity and type of the coin can affect value. Coins that were not released into the general public are categorized as uncirculated and can be worth much more, since they do not have the wear that is common to circulated coins.
Coins that are worth more than their melt value are categorized as collectible coins, and these are coins that collectors actively pursue. For example, many U.S. dimes, quarters and half-dollars minted before 1916 carry a value higher than if they were just melted for their silver content. Coins that were printed with errors can also carry a premium higher than their silver melt value. Coins with off-center printing, coins that were struck twice or three times by the press, or coins with indents are some examples of error coins that can be worth more than coins in normal condition.