if you think about it; come to think of it
Used as a set phrase to introduce a realization or reconsideration, often at the beginning of a sentence.
Come to think of it, he might be right.
If I think about it now, that was the last time.
Kanji spelling for みる; less common and may feel slightly dated or emphatic.
From 考える (to think) in the te-form + みる (to try) in the conditional form みれば, literally 'if one tries thinking about it'.