I am new to the workforce and while my job is totally above board and all the taxes are paid, it is still somewhat informal since I am an hourly-paid nanny for a family. There isn't a clear policy on when to call in sick and when to come in to work. I am granted a limited number of paid (I am paid slightly less than my typical wage for sick days) sick days but I think I might be out of them for now. Back in school, I tended to base my decisions about when to stay home for sickness on how sick I was, but also how much I cared about that specific class.

But these days, every day at work is important, and to ever cancel last minute puts the parents in a tough situation, plus I get paid less than usual even on the paid sick days. So I really don't ever WANT to call in sick because I need the money and I feel awful leaving the parents in the lurch, but when I go to work sick I tend to not get better as soon as I do when I stay home and rest. I have always felt that sick people should stay home and not infect everyone else, but maybe I am just making excuses to lie in bed? I came into work today but I was really considering staying home and giving my cold another day of rest. At the same time, I think if these parents really wanted to shelter their kids even from the common cold, they'd pay me my regular wage to stay home every time I am sick.

My roommate says that you call in sick if you have a fever or are throwing up, but not otherwise. I would absolutely call in sick in those situations (and have), but I wonder if those are really the only times? I have a chronic medical condition that can cause problems at times, and in particular I seem to get more exhausted and weak even with colds than is really typical, so I sometimes feel incapable of doing my job properly even without a fever or vomiting. Of course whether or not you'll get paid, and whether or not you work with immunocompromised people, etc. all can make a difference in how you do things, so how do you handle this?

Tl;dr: what is the adult rule of thumb for when to call in sick? How do I know if I should?