Inputs you will need

To run prejudgment or post-judgment interest for a California matter in DocketMath’s interest calculator, you’ll need a short but precise set of inputs.

Use this as a working checklist:

• Jurisdiction: **California (US-CA)
• Interest type

  • Prejudgment interest
  • Post-judgment interest
  • Contract / other specified rate
• Principal amount (the dollar amount the interest runs on)
• Start date for interest
• End date for interest (or “through” date)
• Interest rate

  • Statutory rate (e.g., default California rate)
  • Contract rate (if applicable)
  • Judgment rate (if a court has specified one)
• Rate type & compounding

  • Simple vs. compound
  • Compounding frequency (if applicable)
• Day-count convention (how days are counted, if you need to match a specific method)
• Partial payments (if any)

  • Amount
  • Date
  • How you want them applied (e.g., interest first, then principal)
• Costs / fees to include in the interest base, if applicable
• Rounding preferences (if you need to match a prior calculation down to the cent)
• Output format

  • Summary only
  • Detailed schedule (per day / per period)

Where to find each input

Below is a practical map of where these inputs usually come from in a California case file, and how they affect your final interest number.

Most inputs live in the case file, contracts, or docket entries. Dates usually come from the triggering event notice; rates and caps come from governing documents or statute; and amounts come from the ledger or judgment. Record the source for each value so the run is reproducible.

Jurisdiction: California (US-CA)

Where to find it

• Caption of the complaint or petition
• Judgment or order
• Case management system entry

Why it matters

• DocketMath uses the jurisdiction to:

  • Load default statutory interest rules for California
  • Label and document your calculation for later reference

Setting US-CA ensures your documentation clearly shows this was a California-specific interest run.

Interest type

Common categories you’ll select in DocketMath:

• Prejudgment interest (before judgment is entered)
• Post-judgment interest (after judgment)
• Contract rate / other specified rate

Where to find it

• Prejudgment vs. post-judgment

  • Procedural posture of the case
  • Judgment date vs. claimed period of damages
• Contract rate

  • Promissory notes
  • Loan agreements
  • Settlement agreements
  • Commercial contracts

How it changes the output

• Different start dates and rates may apply depending on whether it’s:

  • A contract claim with a specified rate
  • A tort claim where statutory rules control
  • Post-judgment interest under California rules

Choosing the correct type keeps your interest period and rate aligned with the underlying authority.

Principal amount

What you enter

• The dollar amount the interest runs on, such as:

  • Unpaid principal balance
  • Damages figure
  • Judgment amount
  • Or a subset of those, depending on your calculation

Where to find it

• Complaint (prayer for relief or damages summary)
• Settlement demands / offers
• Judgment or amended judgment
• Ledger or payoff statement in commercial matters

How it changes the output

• Interest is usually a straight percentage of principal over time. Any error in principal will scale the total interest up or down linearly.
• If you include costs or fees in the principal base, total interest increases; if you exclude them, total interest decreases.

Start date and end date

Start date

**Where to find it (examples)

• Prejudgment

  • Contract-specified accrual date
  • Date of breach
  • Date payment became due
  • Date damages became certain or capable of being made certain (for some California claims)
• Post-judgment

  • Date of entry of judgment (check the clerk’s stamp or docket)

End date (through date)

Where to find it

• Date of:

  • Payment
  • Offer of judgment / settlement
  • A specific cut-off you want to calculate through (e.g., “through 12/31/2025” for a demand letter)

How it changes the output

• Interest in DocketMath is time-based: more days = more interest.
• A one-day shift in either direction can matter, especially on large principal amounts or high rates.

Interest rate

You’ll usually choose between:

• California statutory rate (for the relevant category, if applicable)
• Contract rate (from the agreement)
• Court-specified rate (from an order or judgment)

Where to find it

• Statutory: California codes and case law (often summarized in practice guides; confirm the rule that applies to your claim type and time period)
• Contract:

  • Interest clause in the contract (e.g., “10% per annum”)
  • Default interest provisions (e.g., “18% per annum on all past-due amounts”)
• Court-specified:

  • Judgment
  • Order awarding interest

How it changes the output

• The rate is a direct multiplier:

  • Doubling the rate roughly doubles the interest (for the same principal and time)
  • Small rate differences (e.g., 9% vs. 10%) can compound into large dollar differences over long periods

Rate type & compounding

When you set the rate in DocketMath, you may also specify:

• Simple interest (no compounding)
• Compound interest (interest on interest)
• Compounding frequency (e.g., annual, monthly, daily), if applicable

Where to find it

• Contract provisions (e.g., “interest shall accrue at 12% per annum, compounded monthly”)
• Judgment language
• Governing law or practice for the type of claim, if it addresses compounding

How it changes the output

• Simple interest grows linearly over time.
• Compound interest grows faster, especially over longer periods and higher frequencies.

If the underlying authority is silent on compounding, document your assumption clearly in DocketMath’s notes field.

Day-count convention

Some matters require you to match a specific day-count method, such as:

• Actual/365 (actual days elapsed over 365)
• Actual/360
• 30/360 (each month treated as 30 days)

Where to find it

• Financial contracts and loan agreements
• Bond or note documentation
• Internal firm or client standards for repeat calculations

How it changes the output

• Different conventions can shift the effective rate slightly:

  • Actual/360 generally yields more interest than Actual/365 for the same nominal rate.
  • On small, short-term amounts, the difference is minor; on large, multi-year balances, it can be material.

Partial payments

If the debtor has made payments during the interest period, you’ll want to capture:

• Payment date
• Payment amount
• Application rule (interest first vs. principal first, or as specified)

Where to find it

• Payment history / ledger
• Trust account records
• Client’s internal accounting exports
• Settlement or forbearance agreements that specify how payments are applied

How it changes the output

• Payments reduce the balance that continues to accrue interest.
• Applying payments to interest first vs. to principal first can materially change:

  • Remaining principal
  • Total interest accrued over time

DocketMath lets you enter multiple payments and shows how the balance and interest evolve over time.

Costs, fees, and other add-ons

You may need to decide whether to include:

• Court costs
• Attorneys’ fees
• Late fees or penalties
• Other recoverable amounts

Where to find it

• Judgment breakdown
• Fee and cost awards
• Contract provisions specifying what bears interest

How it changes the output

• If you add them to the interest base, the total interest increases.
• If they do not bear interest under the controlling authority, you’ll typically keep them separate and only calculate interest on the allowed components.

This is a legal interpretation question; DocketMath will run whatever numbers you enter, so you’ll want to document your approach.

Rounding preferences and output format

Rounding

• Some workflows require:

  • Rounding to the nearest cent
  • Truncating at each period
  • Matching a prior statement exactly

Output format

• Summary only: total interest, total amount due
• Detailed schedule: line-by-line breakdown (e.g., per day, per payment, per period)

Where to find it

• Prior calculations you’re trying to match
• Client or internal templates
• Court or agency guidelines for how interest should be presented

How it changes the output

• Rounding rules can cause small differences that matter when you’re reconciling with:

  • Opposing counsel’s numbers
  • Lender statements
  • Prior court filings

DocketMath’s detailed schedule can help you explain or reconcile those differences.

Run it

Once you’ve gathered your inputs, you’re ready to run the calculation in DocketMath:

1. Open the tool

   • Go to the DocketMath interest calculator.

2. Set the jurisdiction and type

   • Select California (US-CA).
   • Choose prejudgment, post-judgment, or contract / specified rate.

Inputs you will need

Use this checklist to gather the core inputs before you run the Interest tool.

• 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

Related reading

For more detail on California interest rules and workflows, see:

• California interest calculations: statutes, rates, and common pitfalls

• Why we started the DocketMath blog

• Why we started the DocketMath blog