1. Condition: The condition of the coin is one of the most important factors in determining its value. Coins that are well-preserved and have sharp details are more valuable than those that are worn or damaged.
2. Mint mark: The mint mark on the coin indicates where it was minted. Coins minted at certain mints, such as the New Orleans mint, can be rarer and therefore more valuable.
3. Rarity: The rarity of the coin also plays a role in determining its value. Some 1842 half dollars are rarer than others, and these rarer coins can command higher prices.
4. Variety: There are several different varieties of the 1842 half dollar, each with its own unique characteristics. Some of these varieties are rarer than others, and these rarer varieties can be more valuable.
5. Market trends: The value of coins can also be influenced by market trends. When the market is strong, prices for coins can be higher, and when the market is weak, prices can be lower.
Based on these factors, the value of an 1842 US half dollar can range from a few hundred dollars to several thousand dollars. It's important to consult with a professional coin dealer or numismatist to get an accurate estimate of the value of your coin.