Ontario Prejudgment
Interest Calculator.
Calculate prejudgment interest under section 128 of the Courts of Justice Act. Enter your dates and the calculator selects the correct quarterly rate automatically — then computes the simple interest owing. Updated for 2026.
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Calculate prejudgment interest
Prejudgment interest is calculated under section 128 of the Courts of Justice Act using the quarterly rate published by the Ontario Ministry of the Attorney General. Enter the date your claim was issued and the calculator picks the right rate for you. For proceedings commenced in 2026, the prejudgment rate is 2.5% (unchanged across Q1–Q3 2026).
Prejudgment Interest Estimator
Enter your claim details below. Fields marked with * are required.
How Ontario prejudgment interest is calculated
Prejudgment interest compensates you for being kept out of your money between the date your cause of action arose and the date the court makes its order. It is governed by section 128 of the Courts of Justice Act and calculated as simple interest at the rate published quarterly by the Ministry of the Attorney General.
The formula
Interest = Principal × Rate × Days ÷ 365
Where Rate is the prejudgment rate for the quarter the proceeding was commenced, and Days is the number of days from the date the cause of action arose to the date of the order. This mirrors the day-count method on the court's own Form 19D (default judgment).
Which quarter's rate applies?
This is the detail most people get wrong. The rate is fixed by the quarter in which the proceeding was commenced — the date the claim was issued by the court — not the quarter when the cause of action arose, and not the rate in effect at the date of judgment. Once set, that single rate applies across the entire prejudgment period.
Key rules for prejudgment interest
- Interest is simple, not compound — it does not accrue on itself
- The rate is locked at the quarterly rate when the proceeding is commenced — it does not fluctuate
- Interest runs from the date the cause of action arose to the date of the order
- If your contract specifies an interest rate, the contractual rate applies instead — enter it in the override field
- Interest should be claimed in the pleading — if it is not pleaded, the court may decline to award it
- The court retains discretion under s. 130 to raise, lower, or disallow interest, or change the period
Current Ontario prejudgment & postjudgment interest rates
The Ontario prejudgment interest rate for Q3 2026 (July 1 – September 30, 2026) is 2.5%. The postjudgment interest rate is 4.0%. The table below shows the official quarterly rates published by the Ministry of the Attorney General for the last three years.
| Quarter | Effective dates | Prejudgment Rate | Postjudgment Rate |
|---|---|---|---|
| Q3 2026 | July 1 – September 30, 2026 | 2.5% | 4.0% |
| Q2 2026 | April 1 – June 30, 2026 | 2.5% | 4.0% |
| Q1 2026 | January 1 – March 31, 2026 | 2.5% | 4.0% |
| Q4 2025 | October 1 – December 31, 2025 | 3.0% | 4.0% |
| Q3 2025 | July 1 – September 30, 2025 | 3.0% | 4.0% |
| Q2 2025 | April 1 – June 30, 2025 | 3.3% | 5.0% |
| Q1 2025 | January 1 – March 31, 2025 | 4.0% | 5.0% |
| Q4 2024 | October 1 – December 31, 2024 | 4.8% | 6.0% |
| Q3 2024 | July 1 – September 30, 2024 | 5.3% | 7.0% |
| Q2 2024 | April 1 – June 30, 2024 | 5.3% | 7.0% |
| Q1 2024 | January 1 – March 31, 2024 | 5.3% | 7.0% |
| Q4 2023 | October 1 – December 31, 2023 | 5.3% | 7.0% |
Source: Ontario Ministry of the Attorney General. The calculator stores the full official series back to 2000. New rates are published quarterly; this table updates when the next quarter's rate is released.
When prejudgment interest is not awarded
Section 128(4) carves out several categories. Prejudgment interest is generally not available on:
- Punitive or exemplary damages
- Interest itself — there is no interest on interest
- Costs of the proceeding
- The portion of an award representing pecuniary loss that arises after the date of the order
- Amounts where interest is otherwise payable as of right (e.g. under a contract that already provides for it)
Personal injury — the 5% rule. In a personal injury action, interest on non-pecuniary (pain and suffering) damages is fixed at 5% per year under Rule 53.10 — not the quarterly table rate. The Court of Appeal confirmed 5% as the presumptive default in 2024. Use the rate override field if you are calculating that head of damages.
Calculating interest for a real claim?
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Prejudgment vs. postjudgment interest
Prejudgment interest covers the period before judgment — from when your claim arose to the date of the order. Postjudgment interest covers the period after, accruing on the amount of the order until it is paid, at a different (higher) rate set by the quarter the order was made. If you already have a judgment, use the Ontario Postjudgment Interest Calculator instead.
Pursuing a smaller debt? The Small Claims Court Calculator rolls interest, court fees, and recoverable costs into a single estimate of what your claim is worth.
Prejudgment interest FAQ
What is prejudgment interest in Ontario?
Prejudgment interest compensates a successful party for being out of pocket between the date their cause of action arose and the date the court makes its order. It is awarded under section 128 of the Courts of Justice Act at the quarterly rate set by the Ministry of the Attorney General, calculated as simple interest.
What is the prejudgment interest rate in Ontario for 2026?
For proceedings commenced in 2026, the Ontario prejudgment interest rate is 2.5% — the rate has held at 2.5% across every published 2026 quarter (Q1–Q3). The rate that applies to your case is the rate for the quarter in which your proceeding was commenced (when the claim was issued), and that rate stays fixed for the whole prejudgment period — it does not change quarter to quarter.
Which date sets the prejudgment interest rate?
The rate is set by the quarter the proceeding was commenced — when the claim was issued by the court — not the quarter when the cause of action arose. Interest still runs from the date the cause of action arose, but the rate itself is locked by the commencement date. That is why this calculator asks for both dates.
Is prejudgment interest simple or compound?
It is simple interest by default — it does not accrue interest on itself. Compound interest is only available where a contract pleaded in the claim provides for it, or in the limited circumstances where a court exercises its discretion under s. 130.
Can I claim prejudgment interest on all of my damages?
No. Under s. 128(4), prejudgment interest is not awarded on punitive or exemplary damages, on interest itself, on costs, or on the part of an award representing pecuniary loss that arises after the order. In a personal injury action, non-pecuniary damages carry a fixed 5% rate under Rule 53.10 rather than the quarterly table rate.
Does prejudgment interest apply in Small Claims Court?
Yes. The Small Claims Court is a branch of the Superior Court of Justice, so s. 128 applies the same way. Remember to claim interest in your Plaintiff's Claim. For a full claim estimate including court fees and recoverable costs, use the Small Claims Court Calculator.
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