A 1977 US $20 bill is worth its face value of $20. Due to their historical significance, some rare series or uncirculated 1977 $20 bills may be worth more to collectors, but they typically fetch prices in the range of $20 to $50. As with all older currency, the condition and rarity of the note will determine its actual value. It's always a good idea to consult with reputable coin and currency dealers or numismatic experts for an accurate assessment of a specific bill's worth.