Please don't assume that because a bill is old it must be a silver certificate. The last $20 silver certificates were printed in the 19th century. Please check the top of your bill to see whether it says "Federal Reserve Note" or "National Currency".
Then post a new question with its seal color, date, and whether there's a small letter next to / under the date. That information is important when determining a value.
You did not supply any information about its date or condition, so my best suggestion would be to look at a site such as: http://www.uscurrencyauctions.com/$20notes.htm
Please don't assume that every old bill must be a silver certificate. The last US $20 silver certificates were printed in 1891. As the green seal and banner across the top of the bill indicate, a 1934 $20 bill is a Federal Reserve Note. There's more information at the question "What is the value of a 1934 US 20 dollar bill?" .
Please check your bill again and post a new, separate question. No US bills are dated 1937, and the last $20 silver certificates were printed in 1891.
Please check your bill again and post a new, separate question.There were no federally-issued $20 bills dated 1920.The last $20 silver certificates had an 1891 series date.
Please check your bill again. The last $20 silver certificates were printed in 1891. If it has a green seal, then as indicated by the banner across the top of the portrait the bill is a Federal Reserve Note. Please see the question "What is the value of a 1928 US 20 dollar bill?" for more information.
Please check your bill again and post a new question. The US didn't issue any bills with that date, and the last $20 silver certificates were dated 1891.
Please don't assume that every old bill is a silver certificate. 1914 $20 bills were issued as Federal Reserve Notes, not silver certificates. There's more information at the question "What is the value of a 1914 US 20 dollar bill?".
these sell for $20-25 in online auctions
$20 to $60 depending on condition
Please don't assume that every old bill must be a silver certificate. The last US $20 silver certificates were printed in 1891. As the green seal and banner across the top of the bill indicate, a 1934 $20 bill is a Federal Reserve Note. There's more information at the question "What is the value of a 1934 US 20 dollar bill?" .
Please don't assume that because a bill is old it must be a silver certificate. The last US $20 silver certificates were printed in 1891. As you can see by the banner across the top of the bill and the green seal, your bill is a Federal Reserve Note. There's more information at the question "What is the value of a 1950 US 20 dollar bill?"
well-worn = $20 lightly worn = $40 crisp uncirculated = $60
The US only issued $1 silver certificates dated 1957. No other denominations have that date. The last $20 silver certificates were issued in the 1891 series.
Please don't assume that every old bill is a silver certificate. As the banner across its top and green seal color indicate, your bill is a Federal Reserve Note, the same kind issued today but with a different design. There's more information the at question "What is the value of a 1963 US 20 dollar bill?".
Please check your bill again and post a new question. The last US $20 silver certificates were printed in 1891, and no $20 bills of any kind were printed in 1953.
The last $20 silver certificates are dated 1891. There are no U.S. bills of any type dated 1955. Please check again and post a new question.
Please check your bill again and post a new, separate question. No US bills are dated 1937, and the last $20 silver certificates were printed in 1891.
As the banner across the top indicates, your bill is actually a Federal Reserve Note. Not all old bills are automatically silver certificates. Please see the question "What is the value of a 1934 US 20 dollar bill with HAWAII on it?" for more information.