Dex and Em's ages at key points in the series reveal their growth and development over time. Emma's tragic death at 36 is a heartbreaking twist after her struggles and growth throughout the series. Dex's journey to acceptance and peace at 42 showcases how age influences his decisions and relationships.

Warning: This article contains Major spoilers for One Day.

Netflix’s One Day spans over two decades, raising the question of how old Emma and Dex are at the start, middle, and end of the story. Based on David Nicholls’ eponymous book that was released in 2009, One Day follows the friendship and love story between Emma “Em” Morley and Dexter “Dex” Mayhew. The pair meet the day of their graduation from the University of Edinburgh on St. Swithin’s Day in 1988, spending the whole day together. One Day revisits Emma and Dexter on St. Swithin’s Day every year for the next two decades.