Something I have learned in time is that savings should be the first item to be deducted from the net monthly income.

So based on this you should go with the following
"formula" (although it might not work for you)

Income - Savings = Expenses

So if you establish your savings plan then you know what is left to be spent.

As said above some people here earn roughly 300 US$ (or even less than that) a month and they still live.

Regards!!