How Our Calculators Are Built & Verified
Every one of our 399+ calculators is built on a named statutory source, cross-verified against official government tools, and refreshed each financial year. This page documents the exact formulas and sources so you can check our work.
Formulas & Statutory Sources
Loan EMI / Mortgage Payments
EMI = P × r × (1+r)ⁿ / ((1+r)ⁿ − 1)
Standard reducing-balance amortisation. r = annual rate ÷ 12 (÷ 2 for Canadian semi-annual compounding, per the Interest Act, s.6).
Sources: RBI Master Directions on Interest Rate on Advances; CFPB Reg Z amortisation rules (USA); FCA MCOB (UK)
SIP / Recurring Investment Returns
FV = A × ((1+i)ⁿ − 1) / i × (1+i)
Annuity-due future value, monthly compounding. Assumes contribution at start of month, consistent with AMFI illustration standards.
Sources: AMFI / SEBI Mutual Fund illustration guidelines
PPF / NSC / Small Savings
NSC: M = P × (1 + r)^n (annual compounding) · PPF: yearly compounding on lowest balance between 5th and month-end
Rates reset quarterly by the Ministry of Finance; each certificate locks its purchase-quarter rate for the full term.
Sources: Ministry of Finance (DEA) quarterly small-savings notifications; Post Office Savings Bank manual
Income Tax (India, USA, UK, Ireland, Canada, Australia)
Progressive slab application with marginal rates, surcharges, cess, and regime-specific deductions
India: both old and new regimes with §87A rebate and marginal relief. USA: federal brackets + standard deduction per annual IRS Rev. Proc. UK: personal allowance taper above £100k. Ireland: USC bands + PRSI.
Sources: Income-tax Act 1961 + annual Finance Act; IRS Revenue Procedures; HMRC rates and thresholds; Revenue.ie; CRA; ATO tax tables
Mortgage Affordability & Regulation
LTI and LTV caps applied per jurisdiction before payment maths
Ireland: Central Bank LTI 4× (FTB) / 3.5×, LTV 90%/80%/70%. UK: FCA stress-test approach. Canada: OSFI B-20 qualifying rate.
Sources: Central Bank of Ireland Macroprudential Measures; FCA MCOB; OSFI Guideline B-20
Retirement / Pension Projections
Corpus = Σ contributions compounded + existing corpus × (1+r)ⁿ, drawdown via annuity PV
Default return assumptions are conservative (equity 10-12% India / 7-10% USA pre-inflation) and user-overridable. We display the assumption in the result, never hide it.
Sources: EPFO/NPS trust statements; SSA actuarial tables; ONS life expectancy data
Health (BMI / BMR / TDEE)
BMI = kg/m² · BMR via Mifflin-St Jeor · TDEE = BMR × activity factor
Mifflin-St Jeor chosen over Harris-Benedict per ADA evidence review. WHO Asian-population BMI cut-offs shown where relevant.
Sources: WHO BMI classification; Mifflin et al. (1990), Am J Clin Nutr
Update Cadence by Country
| Country | Trigger Event | What Gets Updated |
|---|---|---|
| India | Union Budget (Feb) + quarterly small-savings rate resets | New slabs live within 2 weeks of Finance Act assent |
| USA | IRS Revenue Procedure (Oct-Nov) for next tax year | Brackets, standard deduction, 401k/IRA/HSA limits |
| UK | Spring Budget + Autumn Statement | Personal allowance, ISA limits, stamp duty thresholds |
| Ireland | Budget Day (Oct) | USC bands, tax credits, Help-to-Buy parameters |
| Canada | Federal Budget + annual indexation (Jan) | Brackets, TFSA/RRSP limits, OAS clawback threshold |
| Australia | Federal Budget (May) | Tax tables, super guarantee rate, HECS thresholds |
Verification Process
- Cross-checked against official tools — each calculator family is validated against the corresponding government calculator (e.g. IRS Tax Withholding Estimator, HMRC tax calculator, Revenue.ie) before release.
- Regression-tested — formula changes run against a fixture set of known-correct results in CI; a build that changes any verified output fails.
- Assumptions shown, never hidden — every projection displays its rate assumption inline, and rates are user-overridable.
- No advice — we show maths, not recommendations. For decisions, consult a licensed advisor in your jurisdiction.
Corrections
Found an error? Email contact@calccorp.com with the calculator URL and the input values. Verified corrections ship within 72 hours and are noted on the affected page.