The honest arithmetic of working while you study
The number that matters is not your hourly rate. It is the hours the job actually eats.
Most students count a shift as its length. A five hour shift, five hours. It is never five hours. Add the travel there and back, the getting ready, the fifteen minutes of standing outside because you would rather be early than late, and the recovery afterwards when you are technically free but too flat to do anything useful. That five hour shift is closer to seven and a half, and the last of them are the hours you would otherwise have spent doing the thing you moved here for. Do this sum honestly across a week before you agree to a roster, because the version in your head is always the cheaper one.
Then look at the shape, not just the total. The same weekly hours feel completely different depending on how they land. Two long days can be manageable. Five short evenings can be ruinous, because each one costs a full transition and leaves a stump of a night behind it. Late finishes before early starts are the classic trap: they look fine on a roster and they quietly wreck the following day. If you have any say at all in how your hours are arranged, spend that influence on clustering them rather than on the total, because clustering is what buys back usable time.
Finally, know your own limit before you are tested. Decide, in a calm week, how many hours is your ceiling and what the warning signs are that you have passed it: missed classes, chronic lateness, sleeping through mornings, dread on a Sunday, the slow feeling that study has become the thing you fit around work rather than the reverse. Write those signs down. On the day you are being offered extra shifts and the money is right there in front of you, that written list is worth more than your judgement in the moment, which is being paid to say yes.