monthly nut
An individual's fixed monthly expenses, such as rent, utilities, cell phone, Internet access, car payments, car insurance, etc. These are the bills you have to pay regardless of what you do in a particular month. Can also be used more generally to describe one's monthly expenses, regardless of whether they are fixed or variable.
If I'm going to make a living as a jazz trombonist I have to keep my monthly nut small.
Monthly Nut
Nutting Monthly
why hasn't Cindy helped me with the monthly nut?