A U.S. first-class stamp cost $0.13 in 1977.
That 13-cent rate covered a standard domestic first-class letter weighing up to one ounce. The rate took effect in 1975 and remained in place through 1977, before increasing to 15 cents in 1978. The price applied to postage, not to the paper, envelope, or any optional mailing service.
The year can be confusing because the Postal Service issued many different 13-cent stamps during this period, including commemorative designs. A stamp’s artwork or issue date does not necessarily identify the mailing rate by itself, but the 13-cent denomination matched the prevailing first-class letter price.
The rate was set during a period when the U.S. Postal Service was adjusting to the Postal Reorganization Act of 1970, which changed how postal rates were established. In modern terms, the 1977 price was a “nondenominated” historical curiosity only in comparison with today’s Forever stamps: customers then generally bought stamps marked with their exact value.