Fetching details from the dictionary...

at the most; at best
to the utmost; as much as possible; as much as one can
一日にせいぜい二時間しか勉強できない。
I can only study two hours a day at most.
せいぜい頑張ってもこの程度だ。
This is about all I can manage even at my best.
彼が走れるのはせいぜい五キロだ。
He can run five kilometers at most.