Financial Methodology & Precision Policy

1. Arbitrary-Precision Mathematical Policy

Standard JavaScript engines use IEEE-754 double-precision floating-point numbers, which cause microscopic binary conversion errors (e.g., 0.1 + 0.2 = 0.30000000000000004). While negligible in basic math, these errors compound across 360 monthly mortgage payments into dollar-level discrepancies.

Numvero enforces arbitrary-precision decimal arithmetic across all engines via decimal.js configured to 20 decimal places of precision with ROUND_HALF_UP rounding compliant with standard banking practices.

This architectural decision is critical for financial calculations because even a $0.01 rounding difference per month compounds to $3.60 over a 30-year mortgage. Our decimal.js configuration eliminates this drift entirely, ensuring that every amortization schedule, PMI calculation, and interest accrual computation matches bank-grade accounting precision. Each calculation engine operates independently with its own decimal context, preventing cross-contamination between concurrent calculations.

3. Mathematical Assumptions & Default Parameters

Every Numvero calculator uses transparent default assumptions that are clearly disclosed and user-adjustable. The following baseline parameters are applied unless the user modifies them:

• Compounding Frequency: Monthly (12 periods per year) — the standard for US residential mortgages and consumer installment loans.
• Day Count Convention: Actual/365 for daily interest accrual calculations. Leap years use 366 days when applicable.
• PMI Rate Estimation: 0.55% to 1.50% of original loan amount annually, tiered by credit score and LTV ratio per industry standard rate cards.
• Property Tax Estimation: Default 1.25% of home value annually, adjustable by user to match county-specific millage rates.
• Homeowners Insurance: Default $1,200 annually, adjustable by user based on actual policy premiums.
• Rounding Policy: All final displayed values use ROUND_HALF_UP to the nearest cent ($0.01), consistent with banking industry practices.
• Amortization Schedule Generation: Full month-by-month schedules computed with cumulative interest and principal tracking for visual graphing.

These assumptions are designed to provide the most accurate initial estimates for the majority of US borrowers while remaining fully customizable for edge cases, non-standard loan products, and jurisdiction-specific variations.

5. Explainability & Calculation Transparency Engine

Numvero implements a unique Explainability Engine that generates human-readable mathematical breakdowns for every calculation. Rather than presenting opaque output numbers, each calculator produces step-by-step formula derivations showing exactly how each result was computed.

This transparency layer serves multiple purposes: it educates borrowers about the mathematics behind their loan obligations, it enables independent verification of results, and it builds trust through computational accountability. Financial literacy research consistently demonstrates that borrowers who understand their loan mathematics make better financial decisions and are less likely to default on obligations.

The Explainability Engine outputs include: the specific formula applied, substituted numerical values, intermediate computation steps, and final rounded results with rounding audit trails. This level of transparency is unprecedented among consumer financial calculators and aligns with CFPB recommendations for financial education tools.

6. Data Privacy & Calculation Security Policy

All Numvero calculations are performed entirely client-sidewithin the user's web browser. No financial inputs, calculation parameters, or results are ever transmitted to external servers, stored in databases, or shared with third parties. This zero-server-transmission architecture provides the strongest possible privacy guarantee for sensitive financial information.

Calculation engines are loaded as static JavaScript bundles and executed locally using the browser's JavaScript engine. This means your loan amounts, interest rates, income figures, and debt balances never leave your device. There are no cookies tracking financial inputs, no analytics capturing calculation parameters, and no server-side logging of any user financial data.