# interest.law - Legal Interest Calculator

> Professional interest calculator for UK, US, and Canadian legal and commercial claims.

## About

interest.law is a specialized web application that calculates statutory and contractual interest on legal claims. It supports multiple jurisdictions with daily breakdown tables, variable rate handling, and document export capabilities. The tool is designed for legal professionals, accountants, and businesses who need precise interest calculations for litigation, commercial disputes, and debt recovery.

## Core Capabilities

- Calculate interest using jurisdiction-specific statutory rates
- Generate daily interest breakdown tables with running totals
- Handle variable rates that change during the calculation period
- Process interim payments and credits with proper allocation
- Export calculations as PDF or RTF documents
- Share calculation results via unique, persistent links
- Mobile-responsive design with PWA support for offline access

## Supported Jurisdictions and Rate Options

The calculator supports the following jurisdictions with detailed rate options:

### United Kingdom Rate Options

| Rate Basis | Benchmark / Authority | Margin | Compounding |
|------------|----------------------|--------|-------------|
| Judgments Act 1838 | Fixed statutory rate (8% since 1993) | None | Simple |
| Late Payment of Commercial Debts Act 1998 | Bank of England base rate (fixed semi-annually: Jan 1 / Jul 1) | +8% | Simple |
| Bank of England Base Rate | BoE Monetary Policy Committee | User-specified (0% default) | Simple |
| Special Account Rate | Fixed rate for court special accounts | None | Simple |
| User-Specified Rate | User-defined fixed rate | User-defined | Simple or Compound |

**Judgments Act 1838**
- Fixed rate: 8% per annum
- Applies to: Money judgments in England and Wales (High Court and County Court)
- Simple interest calculated daily
- Rate unchanged since 1993

**Late Payment of Commercial Debts Act 1998**
- Rate: Bank of England base rate + 8%
- Rate fixing: Semi-annual (January 1 and July 1)
- Reference dates: December 31 (for H1) and June 30 (for H2)
- Applies to: B2B transactions where payment terms exceeded
- Includes statutory compensation: £40-£100 depending on debt size

**Bank of England Base Rate with Margin**
- Pure BoE base rate as official benchmark
- User can specify any margin (e.g., +2%, +4%, etc.)
- Rate updates automatically when BoE changes base rate
- Useful for contractual interest clauses tied to base rate

**Contract Rate**
- Custom rates as specified in agreements
- Supports both simple and compound interest
- Configurable compounding frequency

### United States Federal Rate Options

| Rate Basis | Benchmark / Authority | Margin | Compounding |
|------------|----------------------|--------|-------------|
| Federal Post-Judgment (28 U.S.C. § 1961) | 1-Year Treasury CMT (weekly auction) | None | Simple |
| Contract Disputes Act (CDA) | Treasury Secretary semi-annual rate | None | Simple (pre-2001) / Compound (post-2001) |
| Prompt Payment Act (PPA) | Treasury semi-annual rate for federal invoices | None | Simple |
| US Prime Rate | Federal Reserve H.15 | User-specified | Simple |
| User-Specified Rate | User-defined fixed rate | User-defined | Simple or Compound |

**Federal Post-Judgment Interest (28 U.S.C. § 1961)**
- Rate: Weekly average 1-year Treasury constant maturity rate
- Source: Federal Reserve Statistical Release H.15
- Rate fixed at: Date judgment is entered
- Applies to: All federal court money judgments
- Calculation: Simple interest

**Contract Disputes Act (CDA) Interest**
- Rate: Treasury Secretary rate published semi-annually
- Applies to: Federal contractor disputes
- Compounding: Simple for claims before Oct 2001; compound thereafter

**Prompt Payment Act (PPA) Interest**
- Rate: Treasury rate for federal invoice payments
- Applies to: Late payments by federal agencies
- Automatic entitlement after due date

### United States State-Specific Rate Options

All 50 states and DC supported with their specific statutory rates:

| State | Rate Basis | Benchmark / Authority | Margin | Notes |
|-------|------------|----------------------|--------|-------|
| Alabama (AL) | Fixed | Statutory | 6% | Fixed rate |
| Alaska (AK) | Federal 1961 | 1-Year Treasury CMT | None | Follows federal rate |
| Arizona (AZ) | Fixed | Statutory | 10% | Fixed rate |
| Arkansas (AR) | Federal Discount | Federal Reserve discount rate | None | Variable |
| California (CA) | Fixed | Statutory | 10% | Fixed rate |
| Colorado (CO) | Fixed | Statutory | 8% | Fixed rate |
| Connecticut (CT) | Fixed | Statutory | 10% | Fixed rate |
| Delaware (DE) | Federal Discount | Fed discount + 5% | +5% | Variable |
| District of Columbia (DC) | Published table | DC Courts | None | Quarterly table |
| Florida (FL) | CFO quarterly | CFO published rate | None | Quarterly variable |
| Georgia (GA) | Prime-based | Prime rate | +3% | Variable |
| Hawaii (HI) | Fixed | Statutory | 10% | Fixed rate |
| Idaho (ID) | T-Bill based | 6-month T-Bill + 5% | +5% | Annual update |
| Illinois (IL) | Fixed | Statutory | 9% post-judgment | Fixed rate |
| Indiana (IN) | Fixed | Statutory | 8% | Fixed rate |
| Iowa (IA) | Treasury-based | Annual treasury rate | None | Annual update |
| Kansas (KS) | Fixed | Statutory | 10% | Fixed rate |
| Kentucky (KY) | Fixed | Statutory | 12% (judgment) | Fixed rate |
| Louisiana (LA) | Fixed | Statutory | Judicial rate | Fixed rate |
| Maine (ME) | Prime-based | Prime rate | +5% or 15% | Higher of options |
| Maryland (MD) | Fixed | Statutory | 10% | Fixed rate |
| Massachusetts (MA) | Fixed | Statutory | 12% | Fixed rate |
| Michigan (MI) | T-Bill based | 6-month T-Bill + 1% | +1% | Variable |
| Minnesota (MN) | Fixed | Statutory | 10% | Fixed rate |
| Mississippi (MS) | Fixed | Statutory | 8% | Fixed rate |
| Missouri (MO) | Fixed | Statutory | 9% | Fixed rate |
| Montana (MT) | Fixed | Statutory | 10% | Fixed rate |
| Nebraska (NE) | Fixed | Statutory | 12% | Fixed rate |
| Nevada (NV) | Prime-based | Prime rate | None | Variable |
| New Hampshire (NH) | Fixed | Statutory | 10% | Fixed rate |
| New Jersey (NJ) | Fixed | Statutory | Special Civil +2% | Varies by court |
| New Mexico (NM) | Fixed | Statutory | 15% | Fixed rate |
| New York (NY) | Fixed | Statutory | 9% | Fixed rate |
| North Carolina (NC) | Fixed | Statutory | 8% | Fixed rate |
| North Dakota (ND) | Fixed | Statutory | 12% | Fixed rate |
| Ohio (OH) | Federal 1961 | 1-Year Treasury CMT | None | Follows federal |
| Oklahoma (OK) | Fixed | Statutory | 6% | Fixed rate |
| Oregon (OR) | Fixed | Statutory | 9% | Fixed rate |
| Pennsylvania (PA) | Mixed | Prime + offset or 6% | Varies | Complex rules |
| Rhode Island (RI) | Fixed | Statutory | 12% | Fixed rate |
| South Carolina (SC) | Fixed | Statutory | 12% (judgment) | Fixed rate |
| South Dakota (SD) | Fixed | Statutory | 12% | Fixed rate |
| Tennessee (TN) | Fixed | Statutory | 10% | Fixed rate |
| Texas (TX) | Prime-based | OCCC published (Prime) | None | Monthly table |
| Utah (UT) | Federal 1961 | 1-Year Treasury CMT | None | Follows federal |
| Vermont (VT) | Fixed | Statutory | 12% | Fixed rate |
| Virginia (VA) | Fixed | Statutory | 6% | Fixed rate |
| Washington (WA) | Prime-based | Prime rate | +2% | Variable |
| West Virginia (WV) | Fixed | Statutory | 10% | Fixed rate |
| Wisconsin (WI) | Prime-based | DFI SOAR published | None | Bi-weekly table |
| Wyoming (WY) | Fixed | Statutory | 10% | Fixed rate |

### Canada Rate Options

| Rate Basis | Benchmark / Authority | Margin | Compounding |
|------------|----------------------|--------|-------------|
| Ontario Pre-Judgment | Ministry of Attorney General quarterly | None | Simple |
| Ontario Post-Judgment | Ministry of Attorney General quarterly | None | Simple |
| British Columbia Pre-Judgment | BC Courts (COIA) quarterly | None | Simple |
| British Columbia Post-Judgment | BC Courts (COIA) quarterly | None | Simple |
| Alberta Prescribed | Judgment Interest Act (annual) | None | Simple |
| Manitoba Quarterly | Court of Queen's Bench Act | None | Simple |
| Bank of Canada Prime | BoC published rate | User-specified | Simple |
| User-Specified Rate | User-defined fixed rate | User-defined | Simple or Compound |

**Federal Court Act**
- Bank of Canada target rate plus statutory margin
- Applies to: Federal Court judgments

**Ontario**
- Quarterly rates set by Ministry of Attorney General
- Separate pre-judgment and post-judgment rates
- Published in advance for each quarter

**British Columbia**
- Court Order Interest Act rates based on prime
- Separate pre-judgment and post-judgment rates
- Quarterly publication by BC Courts

**Alberta**
- Judgment Interest Act prescribed rates
- Annual rate setting

**Manitoba**
- Court of Queen's Bench Act rates
- Quarterly updates

## Rate Sources

All interest rates are sourced from official government publications and synchronized daily:

| Jurisdiction | Source | Update Frequency |
|--------------|--------|------------------|
| UK Base Rate | Bank of England | Daily |
| UK Special Account | Court Funds Office | As announced |
| US Treasury Rates | Federal Reserve H.15 | Weekly |
| US Prime Rate | Federal Reserve H.15 | As announced |
| Federal 1961 Rate | Federal Reserve H.15 | Weekly |
| CDA/PPA Rates | Treasury Fiscal Service | Semi-annually |
| Texas OCCC | Office of Consumer Credit Commissioner | Monthly |
| Florida CFO | Chief Financial Officer | Quarterly |
| DC Courts | DC Courts website | Quarterly |
| Wisconsin DFI | DFI SOAR database | Bi-weekly |
| Canada Prime | Bank of Canada | As announced |
| Ontario Rates | Ministry of Attorney General | Quarterly |
| BC Court Rates | BC Courts | Quarterly |
| Alberta Rates | Alberta Courts | Annually |

## Key Pages

### Calculator Pages (Single-Page Application)
- `/` - UK Interest Calculator (default view)
- `/usa` - US Interest Calculator with state selection dropdown
- `/canada` - Canadian Interest Calculator with provincial selection

### Static HTML Pages
These pages are served as static HTML for optimal SEO and AI crawler access:

- `/methodology/` - Detailed explanation of calculation methods, rate sources, and legal citations
- `/library/` - Index of educational articles on interest calculation topics
- `/pricing/` - Subscription plans and professional features

## Library Articles

Educational articles explaining specific calculation methodologies and legal requirements. All articles available as static HTML:

### US Federal Interest
**`/library/us-federal-post-judgment-interest/`**
Comprehensive guide to 28 U.S.C. § 1961 federal post-judgment interest. Explains the statutory framework, rate determination process, and calculation methodology. Includes worked examples and common pitfalls.

### State-Specific Guides

**`/library/texas-post-judgment/`**
Texas post-judgment interest under Finance Code § 304.003. Covers OCCC rate publications, rate change handling, and the interaction between pre-judgment and post-judgment rates.

**`/library/florida-post-judgment/`**
Florida CFO quarterly rate methodology. Explains the discount rate formula, publication schedule, and calculation examples for Florida Statutes § 55.03.

### UK Interest Guides

**`/library/uk-interest-calculator/`**
Complete guide to UK legal interest covering both Judgments Act 1838 and Late Payment Act 1998. Explains when each applies and how rates are determined.

**`/library/uk-late-payment/`**
Deep dive into the Late Payment of Commercial Debts Act. Answers the common question: does the rate fluctuate with Bank of England changes? (No - it's fixed semi-annually.)

**`/library/uk-special-account-rate/`**
Guide to the Special Account Rate for court-held funds in England and Wales. Explains the Court Funds Office rate, its variable nature, and when it applies.

**`/library/uk-interest-costs/`**
Interest on solicitor-client and party-party costs in litigation. Covers when interest runs and applicable rates.

### Federal Contractor Interest

**`/library/cda-vs-ppa/`**
Contract Disputes Act vs Prompt Payment Act interest comparison. Explains why the same Treasury rate can produce different results depending on the applicable statute.

### General Interest Topics

**`/library/credits-receipts/`**
How to handle interim payments in interest calculations. Covers payment allocation methods, date of receipt vs date of credit, and impact on running balances.

**`/library/wage-arrears/`**
Interest calculations for employment tribunal awards and wage claims. Covers statutory requirements for employment-related interest.

## Calculation Features

### Daily Breakdown Tables
Every calculation produces a period-by-period breakdown showing:
- Date range for each rate period
- Applicable interest rate
- Number of days in period
- Daily interest amount
- Period interest subtotal
- Running interest total
- Running balance (principal + interest)

### Variable Rate Handling
For statutes where rates change during the calculation period (Late Payment Act, quarterly state rates):
- Automatic detection of rate change dates
- Seamless transition between rate periods
- Accurate day counting across boundaries

### Interim Payment Processing
When partial payments are received:
- Proper allocation (typically to interest first, then principal)
- Automatic balance recalculation
- Clear indication in breakdown table

### Document Export
Professional document generation:
- **PDF**: Formatted calculation summary with breakdown table
- **RTF**: Editable format for inclusion in legal documents
- Includes all inputs, methodology notes, and rate citations

### Share Links
- Generate unique URLs for any calculation
- Links persist and can be bookmarked
- Useful for sharing with colleagues or clients

## Technical Specifications

- **Application Type**: React single-page application with static HTML for content pages
- **Data Updates**: Interest rates synchronized daily from official sources
- **Accessibility**: WCAG AA compliant
- **Mobile Support**: Responsive design with Progressive Web App (PWA) support
- **Offline Capability**: Core calculator functions available offline via service worker
- **Browser Support**: All modern browsers (Chrome, Firefox, Safari, Edge)

## API Information

This is a client-side web application. There is no public API. Rate data is fetched from our backend which aggregates official sources.

## Legal Disclaimer

This calculator provides mechanical interest calculations based on user inputs. It does not constitute legal advice and is not a determination of:
- Entitlement to interest
- The applicable interest rate for any specific claim
- The correct start or end date for interest calculation
- Whether statutory or contractual interest applies

Users should verify calculations and consult qualified legal professionals for advice on specific matters.

## Contact

- **Email**: contact@interest.law
- **Website**: https://interest.law

## Site Structure Summary

```
interest.law/
├── /                    → UK Calculator (SPA)
├── /usa                 → US Calculator (SPA)
├── /canada              → Canada Calculator (SPA)
├── /methodology/        → Calculation methodology (static HTML)
├── /library/            → Article index (static HTML)
├── /library/
│   ├── us-federal-post-judgment-interest/
│   ├── texas-post-judgment/
│   ├── florida-post-judgment/
│   ├── uk-interest-calculator/
│   ├── uk-late-payment/
│   ├── uk-special-account-rate/
│   ├── uk-interest-costs/
│   ├── cda-vs-ppa/
│   ├── credits-receipts/
│   └── wage-arrears/
├── /pricing/            → Subscription plans (SPA)
├── /terms/              → Terms of use (SPA)
├── /sitemap.xml         → XML sitemap
├── /robots.txt          → Crawler directives
├── /feed.xml            → RSS feed with article content
└── /llms.txt            → This file
```

## Version

Last updated: 2026-01-19