Minting errors can occur on any half dollar. Specific dates and designs are particularly prone to certain minting mistakes. Below are some key errors (among others) to be vigilant about.

Errors:
1964 "Accented Hair" Kennedy Half Dollar (uncirculated value $50)
1966 "No FG" Kennedy Half Dollar (avg. value $35 to $100)
1972 "Doubled Die Obverse" Kennedy Half Dollar (uncirculated value $300)
1974-D "Doubled Die" Kennedy Half Dollar (avg. value $25 to $75)
1982 "No FG" Kennedy Half Dollar (uncirculated value $50)
1983 "Spitting Eagle" Kennedy Half Dollar (avg. value $10 to $45)
1995 "Double Die Obverse" Kennedy Half Dollar (uncirculated value $50)
2004 "Double Die Obverse" Kennedy Half Dollar (avg. value $20 to $60)
2010 "Doubled Die Reverse" Kennedy Half Dollar (uncirculated value $30)