比不上 / 赶不上 bǐbushàng / gǎnbushàng
比不上 / 赶不上（bǐbushàng / gǎnbushàng）means “'cannot compare with / cannot match / fall behind' — A 比不上/赶不上 B”. Both are potential complements meaning A is inferior to B. Formation: A + 比不上/赶不上 + B（＋方面）（A 不及 B）
'cannot compare with / cannot match / fall behind' — A 比不上/赶不上 B
HSK5Formation
A + 比不上/赶不上 + B（＋方面）（A 不及 B）
Explanation
Both are potential complements meaning A is inferior to B. 比不上 'cannot compare with / is not as good as' contrasts overall quality (我比不上他 'I'm no match for him'). 赶不上 'cannot catch up with / keep pace with' stresses failing to reach a moving standard or missing something in time (赶不上时代 'fall behind the times'; also 赶不上火车 'miss the train'). Their affirmative forms are 比得上 / 赶得上.
Examples
Note
比不上 = quality/level; 赶不上 = pace/timing (also literally 'miss' a train/bus). Negative sentence 不比…上 is wrong.
FAQ
比不上 / 赶不上 — what does it mean and how is it used?
'cannot compare with / cannot match / fall behind' — A 比不上/赶不上 B. Both are potential complements meaning A is inferior to B. 比不上 'cannot compare with / is not as good as' contrasts overall quality (我比不上他 'I'm no match for him'). 赶不上 'cannot catch up with / keep pace with' stresses failing to reach a moving standard or missing something in time (赶不上时代 'fall behind the times'; also 赶不上火车 'miss the train'). Their affirmative forms are 比得上 / 赶得上.
比不上 / 赶不上 — how do you form it?
A + 比不上/赶不上 + B（＋方面）（A 不及 B）
比不上 / 赶不上 — any usage notes?
比不上 = quality/level; 赶不上 = pace/timing (also literally 'miss' a train/bus). Negative sentence 不比…上 is wrong.