If you are working several part-time jobs at the same time, it is best to let your employer know otherwise you may owe some money when you file your taxes. Unless the employer knows about your other job and takes it into account, they will not hold enough taxes back. Everyone has a basic personal amount of income they can make tax-free for the year. If you have several employers at the same time, they may all be giving you credit for the basic personal amount and not deducting enough income taxes from your pay cheque. If you have any subcontract/self-employment earnings, where nobody is deducting and remitting income taxes on your behalf, you will owe the full amount of taxes on that income when you file.