live within (one's) means
To spend less or only as much money as one is earning or is able to pay in order avoid exceeding one's budget or going into debt. You need to start living within your means and avoid making so many frivolous purchases. Being so poor during college taught me how to live within my means.
live within one's means
to spend no more money than one has. We have to struggle to live within our means, but we manage. John is unable to live within his means.