Interest calculation in Canada: judgment and statutory interest

Quick takeaways

Run this scenario in DocketMath using the Interest calculator.

• Canada judgment interest is commonly calculated using the federal Interest Act rate (for courts covered by it), typically applied from the date of the judgment to the date of payment.
• Statutory interest may also apply under specific statutes. Those rules can specify a different rate, a different start date, and sometimes a different method (e.g., simple vs. compounding).
• DocketMath’s interest calculator lets you model the calculation by entering key inputs like principal, start date, end date, and rate, and then computing interest based on the selected day-count convention and style.
• The fastest way to get an accurate number is to confirm the interest regime (judgment interest vs. statute-based interest) and the legally relevant start date—then ensure you’re using the prescribed rate/method.

Inputs you need

Before you run DocketMath’s interest tool (/tools/interest), gather the items below. The exact fields you enter may vary depending on whether you’re modeling judgment interest or statutory interest.

Use this intake checklist as your baseline for Interest work in Canada.

• principal or judgment amount
• interest type (pre- or post-judgment)
• rate and compounding method
• start date and end/as-of date
• payments or credits that reduce principal
• day-count convention

If any of these inputs are uncertain, document the assumption before you run the tool.

Core inputs (used in most interest calculations)

• Typical judgment-interest start: the date of judgment

  • Statutory interest: the start date can be different (often tied to demand, default, breach, or a notice date)
  • Commonly the payment date (or your “as of” date for settlement calculations)
  • For judgment interest: derived from the statutory method (see Sources and references)
  • For statutory interest: taken from the relevant statute/regulation
  • Many scenarios are effectively simple interest, but some regimes or orders may require compounding

Regime-selection inputs (to ensure the right rate/date logic)

• Whether the matter is one where the federal Interest Act applies can depend on the proceeding and forum

  • Having the exact section helps you confirm the rate and trigger date
  • Some judgments include specific language that may affect how interest is calculated (e.g., whether/when interest starts)

Practical tip for repeat calculations

If you’ll update the as of date frequently (e.g., weekly settlement offers), you’ll reduce errors by keeping consistent inputs:

• Principal
• Start date
• Rate

…and only changing the end date. This makes it easier to verify that interest changes are behaving as expected.

How the calculation works

DocketMath’s interest calculator models interest as an accrual over time using the inputs you provide. In general, if the principal stays the same:

• changing the start date or end date changes the number of days, and therefore the interest
• changing the rate changes interest proportionally (under simple interest)

1) Choose the interest regime (and therefore the correct rate)

You generally have two buckets:

A. Judgment interest (commonly tied to the Interest Act)

Where judgment interest applies, the governing authority typically sets the rate and the relevant method. Your goal is to:

• confirm the legal interest rate for the applicable period, and
• confirm the legally correct start date for accrual (often the judgment date)

If the rate can change over time, the most accurate approach is to run calculations for each relevant sub-period (rate A then rate B), if DocketMath supports that workflow in your process (or by running separate scenarios and summing results).

B. Statutory interest (set by a specific statute)

Some statutes specify:

• a fixed annual rate,
• a variable/benchmark-pegged rate, or
• a formula for the rate, plus
• a defined trigger date (e.g., from demand, default, or notice)

For statutory interest, the section number matters as much as the words “statutory interest” in a general sense.

2) Apply day-count logic (day-based accrual)

Most Canadian interest calculations, in practice and for many common scenarios, behave like simple interest on a day basis:

• **Interest = Principal × Annual Rate × (Days / 365)

Some systems use different day-count rules (including leap-year handling) or a different divisor. If DocketMath offers a setting for style/day-count, align it with the controlling rule. If it doesn’t, use its default and keep a note of the assumption in your calculation record.

3) Handle compounding (only if required)

Compounding is not always required. But if the governing law or order requires it, you’ll need:

• the compounding frequency (e.g., annual, monthly), and
• confirmation of when compounding begins (usually aligned with the interest start date)

Selecting a compounding option when the regime requires simple interest can inflate totals—so match the governing method before using a compounding toggle.

4) Convert outputs into settlement-ready figures

DocketMath typically outputs interest accrued over your selected period (and sometimes a combined total including principal). To make settlement discussions easier:

• produce a small set of “as of” scenarios (e.g., end dates a week apart)
• keep principal/start/rate constant
• vary only the end date and compare results

Under simple interest, interest should generally scale in a predictable way with additional days.

Common pitfalls

Use this checklist to catch the issues that most often cause errors in Canadian interest calculations:

• Judgment interest: often the judgment date
• Statutory interest: depends on the statute’s trigger (demand/default/notice/etc.)
• Contractual interest ≠ statutory/judgment interest unless the governing authority says otherwise
• If the rate is variable over time, a single-rate calculation may be inaccurate
• Don’t “stack” judgment interest and statutory interest unless the law/order permits it
• A compounding setting can materially change results for longer periods
• A divisor/day-count convention that differs from the controlling rule can shift totals
• Prefer rounding at the end of the calculation rather than inside intermediate steps
• Interest is time-sensitive—save the exact end date from your run

Pitfall example: A small date shift can matter over large principals. For a 30-day shift at 5% annual on a $500,000 principal, simple-interest math (500,000 × 0.05 × 30/365) is roughly $2,055 of interest difference.

Sources and references

Because interest rules can be court- and statute-specific, tie your rate and start date to the controlling authority. Below are starting points—replace TODOs with the exact provisions applicable to your matter:

• Interest Act (Canada) — TODO: confirm the specific provisions governing judgment interest rate methodology and effective rate determination for your proceeding.
• Rules of court / court-specific practice — TODO: identify the rule(s) that address whether judgment interest applies automatically and how accrual periods are handled.
• Statute governing your statutory interest — TODO: cite the exact section that states (1) the rate and (2) the start-date trigger (e.g., demand/default/notice).

If you’re not sure which rule applies, it’s better to pause and confirm before relying on the number in settlement discussions.

Start with the primary authority for Canada and confirm the effective date before relying on any output. If the rule has been amended, update the inputs and rerun the calculation.

• Courts of Justice Act (ON), ss. 127-130; Interest Act, R.S.C. 1985, c. I-15

Next steps

1. Open DocketMath’s interest tool: /tools/interest.
2. Enter fields in this order (to reduce input mistakes):

   • Principal
   • Start date
   • End date (your “as of” date)
   • Annual rate
   • Calculation style (simple vs. compounding, if available)
3. Validate the behavior with at least two runs:

   • Use two nearby end dates (e.g., one week apart)
   • Under simple interest, interest should increase consistently with extra days
4. Record your run details:

   • Save the inputs (or screenshot/export) including the exact dates and rate used
5. If the legal rate changes during the period:

   • Split the timeframe into segments (rate A then rate B) and run separate calculations, then sum
6. For statutory interest:

   • re-check the statute’s trigger date (demand/notice/default/breach) vs. judgment date

Related reading

• Interest rule lens: Maine — The rule in plain language and why it matters
• Common interest mistakes in Rhode Island — Common errors and how to avoid them
• Worked example: interest in Maine — Worked example with real statute citations