tighten your belt

to spend less money than you did before because you have less money

勒紧裤带，省吃俭用

I've had to tighten my belt since I stopped working full-time.

自从我停止全职工作以来，就不得不勒紧裤带过日子。

Clearly, if you are spending more than your income, you'll need to tighten your belt.

明摆着，要是你入不敷出，你就得省着点了。