"Good Day Sunshine" was written by McCartney, whose piano playing dominates the recording. The track was one of several contemporary songs that evoked the unusually hot and sunny English summer of 1966. Music critic Richie Unterberger describes it as a song that conveys "one of the first fine days of spring, just after you've fallen in love or started a vacation". Overdubbed by Martin, the piano solo on the track recalls the ragtime style of Scott Joplin. The song ends with group harmonies repeating the title phrase, creating an effect that Riley likens to a "cascade" of voices "enter from different directions, like sun peeping through the trees".