Ontario Pre-Judgment Interest Calculator

Prejudgment interest compensates a successful party for being kept out of their money between the date the cause of action arose and the date the court makes its order. In Ontario it is awarded under section 128 of the Courts of Justice Act and calculated as simple interest at the quarterly rate published by the Ministry of the Attorney General.

For the third quarter of 2026, the prejudgment interest rate in Ontario is 2.5% per annum. This is the official rate published by the Ministry of the Attorney General, and it is read from the same rate table the calculator above uses so the two stay consistent.

This calculator sets the rate using the date the claim was issued — the quarter in which the proceeding was commenced. That single rate then applies across the whole period: interest runs from the date the cause of action arose to the date of the court's order.

It is simple interest by default — it does not accrue interest on itself. Compound interest is only available in limited circumstances, such as where a contract pleaded in the claim provides for it.

No. Under section 128(4) of the Courts of Justice Act, prejudgment interest is generally not awarded on punitive or exemplary damages, on interest itself, on costs, or on the portion of an award representing pecuniary loss that arises after the date of the order.

Yes. The Small Claims Court is a branch of the Superior Court of Justice, so section 128 applies. Interest should be claimed in the Plaintiff's Claim.

It runs from the date the cause of action arose — for example, the date a contract was breached or the date a loss was suffered — up to the date of the court's order. It does not run only from the date you filed your claim.

Multiply the principal amount by the annual rate, divide by 365, and multiply by the number of days between the date the cause of action arose and the date of the order. Because it is simple interest, you do not compound it. The calculator above does this automatically using the official quarterly rate.

For most claims, a single rate applies for the whole period — the rate in effect in the quarter the proceeding was commenced. The rate does not reset each quarter as the case goes on, which is why the calculator uses the claim-issue date to set the rate.

Yes. You should plead and claim prejudgment interest in your Plaintiff's Claim or statement of claim. While courts often award it as a matter of course, the safest practice is to claim it expressly so there is no question it is on the table.

Yes. Under section 130 of the Courts of Justice Act, the court has discretion to raise or lower the rate or change the period, considering factors such as changes in market interest rates, the circumstances of the case, and the conduct of the parties (for example, unreasonable delay).

Historically a distinct rate has applied to non-pecuniary loss in personal injury cases, separate from the quarterly rate used for most other claims. If your claim includes pain-and-suffering damages, confirm which rate applies to that portion, as it can differ from the figure this calculator uses for general claims.

Yes. If a contract sets its own interest rate, that contractual rate generally governs instead of the default Courts of Justice Act rate, and compound interest may be available where the contract provides for it. Enter the applicable rate where your agreement specifies one.

Prejudgment interest compensates you for the period before the court's order (from when the cause of action arose to the date of judgment). Post-judgment interest runs after the order, on the unpaid judgment, until it is paid. They use separate rate tables and separate calculations.

No. Under section 128(4), prejudgment interest is generally not awarded on costs, on interest itself, on punitive or exemplary damages, or on the part of an award for pecuniary loss arising after the date of the order.

The calculator gives a reliable estimate for planning, but the exact interest a court awards can turn on the correct start date, the right rate for your type of claim, and the court's discretion. For anything significant it is worth having a lawyer confirm the figure and how to plead it. Our team offers a free consultation.