差点儿 / 差一点儿【chàdiǎnr / chà yìdiǎnr】

差点儿 means "nearly": it came close, and then didn't happen. It goes after the subject and before the verb, and the sentence often ends in 了. 差一点儿 and 差点 are the same word.

Adding 没

With something you didn't want – being late, falling, forgetting – 没 changes nothing. Both sentences say you weren't late.

With something you did want, 没 matters. 差点儿没 means it only just happened; 差点儿 + 就 means it nearly happened but didn't.

For a hoped-for result, 就 is usually there to make the regret clear.

差点儿 or 差不多

Both contain 差, and learners swap them. 差不多 is "about" with a number, or "much the same"; it doesn't say something nearly happened.

• × 我差不多迟到了 → 我差点儿迟到了

English "barely" also means "hardly at all". 差点儿没 never means that.

• × 我昨天差点儿没吃饭 (meaning "ate very little") → 我昨天没怎么吃饭