If you miss the filing deadline and you have a balance owing for the tax year, CRA charges a penalty of 5% of your balance owing, plus 1% of your balance owing for each full month that your return is late, to a maximum of 12 months.
If you have a balance owing and you miss the payment deadline, CRA charges compound daily interest on your balance owing starting the day after the balance is due. CRA also charges interest on the penalties applied to late returns.
Your late-filing penalty may be higher if you were charged a late-filing penalty on a return for any of the three previous years.