Kennedy half-dollar coins minted in 1964 are 90 percent silver. Kennedy coins from 1965, 1966 and 1967 have high silver percentages, but the silver content of these half-dollar coins decreases every year until the coins are completely made of copper in 1970. So, the earlier the year, the more valuable the coin.
If you’re just looking for melt value, look for coins in the earliest year ranges.