All Schwinn serial numbers before August 17, 1948 were lost in an office fire. Serial numbers were under the bottom hanger bracket until 1952 when they were moved to the left rear dropout. They were moved again in 1972 to the head tube. Several different numbering systems were used and sometimes the same numbers were reused in different years.

• 1948
• 1949
• 1950
• 1951
• 1952
• 1953
• 1954
• 1955
• 1956
• 1957
• 1958

New numbering system: First letter is the month; first digit is the year.

• D836694 = April 1958
• 1959 - A900000…
• 1960 - A000000…
• 1961 - A100000…
• 1962 - A200000…
• 1963 - A300000…
• 1964 - A400000…

New numbering system: First letter = month; second letter = year. I and O skipped to avoid confusion with one and zero.

• 1965 - AA00000…
• 1966 -AB00000…
• 1967 -AC00000…
• 1968 - AD00000…
• 1969 -AE00000…
• 1970 - AF00000…
• 1971 - AG00000…

Serial Number moved to Head Tube

• 1972 - AH00000…
• 1973 - AJ00000…
• 1974 - AK00000…
• 1975 - AL00000…
• 1976 - AM00000…
• 1977 - AN00000…
• 1978 - AP00000…
• 1979 - AQ00000…
• 1980 - AR00000…
• 1981 - AS00000…
• 1982 - AT00000…

This information was taken from The Bicycle Trader August 1996, The West Coaster May/June 1991, and Collectable Schwinn-Built Bicycles by James L. Hurd.