When your net tax owing is more than $3,000.
If your net tax owing is more than $3,000 on your personal tax return, you need to make quarterly instalments. Your tax instalments will cover any amounts owing for the upcoming tax year.
Your tax instalments are based on your prior year's tax amount owing. If you really want to get specific on the amounts, you can use the CRA’s calculation sheet to determine how much you will owe. If you you expect your 2019 tax owing will be similar to 2018, then just use your 2018 tax owing, and divide it into four equal payments. Adjust up or down if you expect your current year amount owing to be higher or lower than your prior year.
These instalments are due on March 15, June 15, September 15 and December 15 (or the next business day if the 15th falls on a weekend or holiday). If you have missed the first couple payments, you can add them to your third payment.