What it means
せいぜい indicates an upper limit or the best realistic result. It is commonly used before a number, amount, duration, or other quantity to mean “at most.” Depending on context, it can also mean “at best,” emphasizing that the result is limited or not especially good. It usually modifies the quantity directly and does not itself change for politeness.
Usage note
せいぜい describes a maximum, so it is different from 少なくとも, which means “at least.” It can sound modest or pessimistic when describing an expected result.
How to use it
参加者はせいぜい三人でした。
There were at most three participants.
参加者はせいぜい三人だった。
There were at most three participants.
Example sentences
この古い扇風機は、せいぜいあと二年使えるでしょう。
This old electric fan will be usable for at most two more years.
この箱には、せいぜい十冊の本しか入りません。
This box can hold at most ten books.
災害に備えて、食料はせいぜい三日分しかありません。
In preparation for disasters, there is only at most three days' worth of food.
この坂を自転車