Formula Sources by Category
Every formula we use comes from an authoritative official source. We do not reverse-engineer or estimate formulas independently.
| Category | Primary Source |
|---|---|
| Income Tax (Old & New Regime) | Income Tax Department India — Finance Act, CBDT Circulars |
| EPF / Employee Provident Fund | EPFO — EPF & MP Act, Annual Circular on interest rates |
| NPS / National Pension System | PFRDA — NPS scheme documents |
| PPF, SCSS, SSY, NSC, KVP, POMIS | Ministry of Finance — Quarterly interest rate notifications |
| GST | GST Council — Rate schedules, CBIC notifications |
| Home & Car Loans (EMI) | Standard reducing-balance formula (RBI guidelines for amortisation) |
| BMI (Indian population) | WHO — Asia-Pacific BMI thresholds (2000), Ministry of Health |
| Calorie / BMR | Mifflin et al. (1990) — Mifflin-St Jeor Equation, peer-reviewed |
| Body Fat % (Navy Method) | Hodgdon & Beckett (1984), U.S. Navy circumference method |
| NPK / Crop recommendations | ICAR — Crop-specific nutrient management guidelines |
| Crypto / VDA Tax | Finance Act 2022 — Section 115BBH, Section 194S |
| Capital Gains Tax | Income Tax Act — Sections 111A, 112, 112A (as amended by Finance Act 2024) |
Our Verification Process
Step 1 — Formula implementation
We implement the formula exactly as published in the official source, including edge cases (partial years, pro-rated amounts, special categories).
Step 2 — Cross-check against official calculators
Where the government provides an official online calculator (e.g., the Income Tax Department's tax calculator at incometax.gov.in), we test our output against it using at least 5 different input scenarios covering different income levels and deduction combinations.
Step 3 — Independent calculation check
We manually calculate expected outputs using the official formula for the same test inputs, and verify our calculator matches.
Step 4 — Edge case testing
We test boundary conditions: minimum/maximum allowed values, zero inputs, and common real-world scenarios that could produce unexpected results (e.g., HRA exemption when employer city differs from rented city, crypto loss carry-forward rules).
Update Schedule
- Tax slabs and rates: Updated within 48 hours of Union Budget announcement
- Small savings scheme rates (PPF, SCSS, SSY etc.): Updated within 7 days of quarterly government notification
- EPF interest rate: Updated within 7 days of EPFO board announcement
- NPS asset allocation and annuity rates: Updated quarterly
- Health formulas (BMI thresholds, BMR equations): Reviewed annually against latest WHO/ICMR guidelines
Known Limitations
We believe in being upfront about what our calculators cannot do:
- Tax calculators assume inputs are accurate and complete — they cannot account for unreported income, complex international taxation, or tax treaty provisions
- Investment return projections use assumed rates — actual mutual fund returns vary and past performance does not guarantee future results
- Health calculators provide estimates based on statistical averages — individual variation in metabolism, body composition, and medical conditions can cause significant deviation
- Loan calculators assume fixed interest rates throughout tenure — floating-rate loans will differ as rates change
Report an Error
Found a calculation that doesn't match an official source? Contact us with the page name, the inputs you used, the output you got, and the correct expected output with your source. We review all reports within 48 hours.