Belly Conklin celebrates her 22nd birthday in The Summer I Turned Pretty season 3’s finale.
The birthday occurs in episode 11, “At Last,” during Belly’s life in Paris. Conrad visits her while traveling onward to Brussels, and Belly invites him to a birthday dinner with her friends. Their day together becomes the emotional centerpiece of the finale.
The age matters because season 3 includes several time jumps. Earlier in the season, Belly turns 21 and becomes engaged to Jeremiah. By the finale, the story has moved forward through her Paris year, online college classes, new friendships, and changing plans, placing her at age 22.
The number can be confused with 21 because that birthday is a prominent earlier event in the season. The season 3 episode synopsis specifically distinguishes the two milestones: Belly turns 21 in episode 4 and celebrates her 22nd birthday in episode 11.