My mother-in-law lives with us. If she pays part of the mortgage, electricity, etc., is that rent? Does it count as a gift to us and thus we should keep it to the limit

[NCperson]

@hellolami it is NOT a gift.  A gift is something given and nothing is received in return.  In this case, something is received in return - a place to live! 

Technically, it is rent income to you.

[Hal_Al]

If this is merely a cost sharing arrangement where the amount paid is below fair market rental, there would be no reportable rental income to you. If the amount is fair market value, or more, there is still some question as to whether you even have to report it, as it almost always comes out zero. Most people take the attitude that it is not income; it's just room mates sharing expenses and ignore it. Family, as opposed to unrelated roommates, makes that position stronger.