1. Mint Mark: The mint mark located on the reverse of the half dollar indicates the mint that produced it. The 1966 US half dollar was struck at three mints: Philadelphia (no mint mark), Denver ("D"), and San Francisco ("S"). The Philadelphia mint produced the majority of half dollars, so examples without a mint mark are more common and less valuable. However, half dollars struck at the Denver and San Francisco mints may have slightly higher value due to their lower mintage numbers compared to the Philadelphia mint.
2. Condition: The physical condition of the coin greatly affects its value. Half dollars in excellent condition with minimal wear, sharp details, and a lustrous appearance are more valuable. Factors like scratches, nicks, dents, discoloration, and cleaning can diminish the value.
3. Variety: The 1966 US half dollar does not have any recognized significant varieties or errors that noticeably impact its value.
4. Special Sets and Commemorative Issues: If the 1966 half dollar is part of a special set, such as a mint or proof set, or if it's a commemorative issue, its value can be higher than its face value.
5. Numismatic Value: For coin collectors, certain 1966 half dollars with exceptional quality or rarity may hold numismatic value. If you believe your half dollar has unique features or historical significance, it's worth consulting a numismatic expert or grading service for a professional evaluation.
Considering these factors, the majority of 1966 half dollars are commonly found in circulation and are valued at their face value. However, if you have a coin in exceptional condition, from a lower mintage mint, or part of a special set, it could be worth more to collectors.