量入为出

liàng rù wéi chū

to assess one's income and spend accordingly (idiom); to live within one's means

You can only spend what you earn.

量

liàng

capacity

入

rù

to enter; to go into

为

wéi

variant of 為|为[wei2]

出

chū

variant of 出[chu1] (classifier for plays or chapters of classical novels)