linguistic:paraphrasing, quality:correction
1970s–1990s

In 1975, the panel format was shortened slightly horizontally, and shortly thereafter the lettering became larger to compensate. Previously, the daily Peanuts strips were formatted in a four-panel "space saving" format beginning in the 1950s, with a few very rare eight-panel strips, that still fit into the four-panel mold. Beginning on Leap Day in 1988, Schulz abandoned the four-panel format in favor of three-panel dailies and occasionally used the entire length of the strip as one panel, partly for experimentation, but also to combat the dwindling size of the comics page.

In the late 1970s, during Schulz's negotiations with United Feature Syndicate over a new contract, syndicate president William C. Payette hired superhero comic artist Al Plastino to draw a backlog of Peanuts strips to hold in reserve in case Schulz left the strip. When Schulz and the syndicate reached a successful agreement, United Media stored these unpublished strips, the existence of which eventually became public. Plastino himself also claimed to have ghostwritten for Schulz while Schulz underwent heart surgery in 1983.

In the 1980s and the 1990s, the strip remained the most popular comic in history, even though other comics, such as Garfield and Calvin and Hobbes, rivaled Peanuts in popularity. Schulz continued to write the strip until announcing his retirement on December 14, 1999, due to his failing health.