CRA Arrears Interest Calculator

Subsection 161(1) of the Income Tax Act charges interest at the prescribed rate on whatever tax remains unpaid after your balance-due day, for as long as it stays outstanding. Subsection 248(11) then says that interest has to be compounded daily — and that once a day’s interest goes unpaid it starts earning daily-compounded interest of its own. CRA states the same thing in plainer words: compound daily interest starts the day after the due date and applies to any unpaid amount, including amounts arising from a reassessment.

Practically, that means the balance you owe on day 90 is not the balance you owed on day 1. This calculator rebuilds the debt one day at a time rather than applying a flat annual percentage, which is why the figure it produces is slightly higher than a simple-interest estimate over the same period.

Which date belongs in “payment due date”

For most individuals the balance-due day for the 2025 tax year was 30 April 2026, and interest runs from 1 May. Being self-employed changes the filing deadline to 15 June but not the payment deadline: CRA is explicit that a balance owing is still due on or before 30 April. If a due date falls on a Saturday, Sunday or public holiday, a payment received on the first business day after is on time. Where the amount comes from a reassessment rather than the original return, interest still runs from the original balance-due day, not from the date of the notice — which is how a small reassessment two years later arrives with a disproportionate interest charge attached.

What the quarterly reset does to a debt that spans quarters

CRA re-sets its prescribed rates every calendar quarter, so the rate is not locked in on the day you miss the deadline. Each day of your debt is charged at the overdue tier in force for the quarter that day falls in, and the result panel breaks the total into one segment per quarter so you can see where the cost accumulated. A balance carried from the spring deadline into the autumn can easily cross two rate changes.

Because CRA publishes each quarter only a few weeks before it starts, any day beyond the last announced quarter is estimated at the most recent published rate and labelled as an estimate in the segment table. Treat those rows as a projection, not a quote. The dates this calculator accepts are limited to 2026.

Interest is not the only charge

Filing late when you owe adds a penalty of 5% of the balance plus 1% for each full month the return is late, up to 12 months — or 10% plus 2% a month for up to 20 months if CRA issued a demand to file and penalised you in any of the three preceding years. That penalty then carries its own interest under subsection 161(11), running from the filing due date to the day it is paid. None of that is in the figure above, which models interest on the balance alone, so file on time even when you cannot pay: it is the cheapest single decision available once you are already late.

Asking CRA to cancel it

The taxpayer relief provisions let CRA cancel or waive interest when something outside your control stopped you from paying. CRA groups the usual grounds as extraordinary circumstances (illness, accident, a death in the immediate family, a disaster or a service disruption), an inability to pay or financial hardship, and errors or delays by CRA itself. The window is strict: a request can only reach interest that accrued during the 10 calendar years before the year in which you make it, so a 2026 request cannot touch interest that accrued in 2015 or earlier.

Apply through “Request relief of penalties and interest” in My Account, or on Form RC4288 by mail; CRA is currently warning that these requests are taking well over a year to work through, and relief does not stop interest accruing while you wait. One small mercy sits in section 161.3: if you pay everything owing other than interest and penalty, and the total interest and penalty for that year is $25 or less, CRA may simply cancel it.