How To Date U.S. Postcards by Postage Amount

You can approximate the date a postcard was manufactured by the amount of postage required to mail it.  If unused, the stampbox usually has the postage requirements.  You can also use this chart if the postcard is used, but with an unreadable postmark date.  However, keep in mind that a postcard might be postally used many years after manufacture, or someone may have used a higher denomination stamp than was required.

  Postage Rate     Valid for Years  
One Cent 1898 - 1917
1919 - 1925
1928 - 1951
Two Cents 1917 - 1919
1925 - 1928
1952 - 1958
Three Cents 1958 - 1962
Four Cents 1963 - 1967
Five Cents 1968 - May 1971
Six Cents May 1971 - Mar 1974
Seven Cents Sep 1975 - Dec 1975
Eight Cents Mar 1974 - Sep 1975
Nine Cents 1976 - May 1978
Ten Cents May 1978 - Mar 1981
Twelve Cents Mar to Oct 1981
Thirteen Cents Nov 1981 - Feb 1985
Fourteen Cents Feb 1985 - Apr 1988
Fifteen Cents Apr 1988 - Feb 1991
Nineteen Cents Feb 1991 - 1994
Twenty Cents 1995 - Jun 2001
Twenty-One Cents Jul 2001 - Jun 2002
Twenty-Three Cents Jul 2002 - Dec 2005
Twenty-Four Cents Jan 2006 - May 2007
Twenty-Six Cents May 2007 -

Another clue to postcard manufacture can be found in the address of the publisher.  Two-digit postal zones were introduced in 1943, and were in-between the city and state, such as Des Moines 17, Iowa.  5-digit ZIP codes were introduced in Jan 1963, and follow the state, such as Des Moines, Iowa 50304.  Zip + 4 codes were introduced in Oct 1983, such as Des Moines, Iowa 50304-0943.