几乎和差不多：

相同点 similarity

副词，两者都表示非常接近、相近，都可以做状语

Both are adverbs, indicating being very close or similar and can serve as an adverbial modifier.

他汉语说得很好，差不多/几乎和中国人一样。

不同点 Differences

“差不多”做副词时，可以直接用在单音节

形容词前，而“几乎”后面的形容词之前或之后要加别的词语。

As adverb,"差不多“can be used right before a monosyllabic adjectives, while before and after the adjective following "几乎”， there must be other words.

他俩差不多高。

他们俩几乎一样高。

他比我几乎高了一头。

“差不多”可以用在数量词前面，表示接近这个数量；“几乎“没有这个用法。

“差不多” can precede a numeral-classifier compound, indicating being close to this quantity, while "几乎" has no such usage.

李老师差不多六十岁了。

"差不多"还可以是形容词，做谓语，表示相差不远，很接近；“几乎“没有这个用法。

“差不多”can also be used as an adjective to serve as the predicate

, indicating being similar and without much difference, while "几乎“ has no such usage.

姐妹俩性格差不多。

“几乎”可以表示说话人不希望发生的事接近实现，但最后没有实现；“差不多"没有这个用法。

“几乎”can indicate something undesirable almost happened, yet finally didin't; "差不多“ has no such usage.

这件事我几乎忘了告诉你了。