Why interest results differ in New York

The top 5 reasons results differ

Run this scenario in DocketMath using the Interest calculator.

If you’re seeing mismatched interest results in New York from DocketMath’s /tools/interest output, the difference usually comes down to one of these five variables. New York’s baseline limits matter too: the general default statute of limitations (SOL) period is 5 years under N.Y. Crim. Proc. Law § 30.10(2)(c) as a general rule. In other words, your interest can diverge when the calculator is using a different “start point” (or when a different time window is being assumed).

Here are the most common drivers:

1. Different start dates used for interest accrual

   • Example: one workflow uses an “event date” (like demand/notice), another uses a later “payment date” or “judgment date.”
   • Even a single day shift can change day-count interest.

2. Day-count convention mismatches

   • Some systems compute interest using actual days; others use a simplified convention (or round interim values).
   • A 365 vs. 360 approach (or rounding at different steps) can visibly change the total.

3. Compounding vs. simple interest

   • If one method compounds interest periodically (monthly/quarterly) and another applies simple interest across the whole period, totals will differ quickly—especially over multi-year spans.

4. Payment allocation assumptions

   • If you input partial payments, the ordering matters:

     • payment applied first to interest, then principal; or
     • payment applied first to principal, then interest.
   • That allocation changes the remaining principal balance at each interest calculation segment.

5. SOL window trimming

   • Because New York’s general default SOL period is 5 years (via N.Y. Crim. Proc. Law § 30.10(2)(c)), interest sometimes gets calculated only within a chosen window.
   • Clear takeaway: The 5-year period described here is the general/default SOL period (not a claim-type-specific rule). If one calculation includes transactions older than 5 years and another trims them, you’ll see consistent—but very different—interest totals.

How to isolate the variable

Use this quick diagnostic workflow to identify exactly which input/convention is causing the divergence. Start with a controlled run where only one factor changes.

• Freeze the jurisdiction and tool settings so both runs use the same rule set.
• Compare one input at a time (dates, rates, amounts) and re-run after each change.
• Review the breakdown to see which segment or assumption drives the difference.

1) Freeze all inputs except one

• Keep constant:

  • Principal amount
  • Interest rate
  • Compounding setting (or compounding frequency if applicable)
  • Any payment schedule
• Change only one of these between runs:

  • Start date
  • End date
  • Day-count/rounding approach (if your alternate system uses a different convention)

2) Compare results and look for patterns

Use these “pattern checks”:

3) Confirm SOL window assumptions (general/default 5-year rule)

Because New York’s general default SOL period is 5 years under N.Y. Crim. Proc. Law § 30.10(2)(c), verify whether the other calculation is:

• calculating interest across the entire timeline, or
• limiting the calculation to a 5-year window aligned to the general/default rule.

If the other system is trimming older transactions, you may see the mismatch appear “suddenly” rather than gradually.

4) Run a “minimal input” test in DocketMath

If the discrepancy persists, strip the scenario down:

• one principal amount
• one date range
• no payments
• fixed rate

Then reintroduce payments and special settings one at a time.

For a fast recalculation, use DocketMath’s Interest tool here: /tools/interest.

Next steps

Once you’ve identified the variable, you can make the two computations consistent without guessing. Here’s a practical checklist:

If you want a reproducible baseline, create two runs in DocketMath:

1. Baseline: no payments, single date range, chosen rate
2. Scenario: add payments and any special date logic

Then compare step-by-step totals to see exactly where the divergence begins.

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