expression
day by day; with each passing day
Describes a gradual change or progression as days pass. Often used with verbs of change like 増す, 強まる, 回復する.
See also: 日を追って
日を追うごとに暑さが増している。
The heat is increasing day by day.
彼の病状は日を追うごとに回復に向かっている。
His condition is improving with each passing day.
Phrase composed of 日 (day), を (object marker), 追う (to follow/chase), and ごとに (each time). Literally 'each time following the day', expressing progression over successive days.