How We Verify Formulas

Accuracy is the only feature that matters in a calculator. This page documents the review, testing and update process every formula passes before it goes live.

1. Formula review process

Locate the formula in a primary source (regulator, scheme operator, standards body, textbook of record).
Cross-check against at least one independent primary source where possible.
Translate the formula into the calculator's input vocabulary, preserving units and conventions.
Document the formula, every variable and every assumption on the published page.

2. Testing methodology

Each calculator ships with a Vitest unit-test file covering:

Reference cases — values published by the official source or computed by hand are reproduced exactly.
Boundary cases — minimum / maximum statutory limits, zero, very large numbers.
Invalid input cases — negative values, non-numeric input, out-of-range tenures. The calculator must throw a readable error.

Tests run on every code change. A calculator cannot be released if any test fails.

3. Edge-case testing

Currency rounding and the IEEE-754 floating-point trap (we round at display time only).
Tenure expressed in months vs years.
Compounding frequency boundaries (annual / quarterly / monthly).
Leap years for date-sensitive calculators.
Locale-specific number formatting (en-IN, en-US, en-GB).

4. Accuracy verification

Where the issuing body publishes its own calculator (e.g. India Post, NPS Trust, EPFO, RBI EMI tools), our output is benchmarked against those tools for a battery of representative inputs. Discrepancies of more than ₹1 / 1 unit are investigated before release.

5. Update procedures

Statutory rates (PPF, EPF, SCSS, MIS, Post Office TD/RD, NPS, SSY, APY) are reviewed when the Ministry of Finance publishes the quarterly notification, and at least once per quarter.
Bank FD default rates are reviewed at least twice a year against the bank's published rate card.
Health and tax constants are reviewed annually against the issuing authority (WHO, IRS, HMRC, ATO, CBDT).
Every change is logged in the migration history; users always see the latest reviewed value.

Reporting an error: If you believe a formula or default rate is incorrect, please email support@creditloancalculator.com with the calculator URL and the source you'd like us to verify against. We acknowledge formula reports within 2 business days.