How CalculatorKosh Calculates
We show our work. Every number on CalculatorKosh comes from a published formula or an official Indian source — never a black box. You should never have to take our word for it, so this page lays out exactly how each kind of calculator works and where the rules come from. If a figure ever looks off, you can trace it back to its source and check it yourself.
Our principles
- Real formulas, not estimates. Each tool implements the actual mathematical or statutory formula, tested against worked examples.
- Official sources. Tax, rates and health thresholds follow the bodies that set them in India — not generic global defaults.
- Kept current. When a rule changes — a Budget, a new slab, a revised rate — we update the tool and stamp the page.
- Independent & private. We're not a bank, broker or advisor. Calculations run in your browser; nothing you enter is stored or sent anywhere.
Method by category
Income tax & salary
We apply the income-tax slabs, standard deduction, Section 87A rebate, surcharge and 4% health-and-education cess for the financial year you select, under both the old and new regimes, exactly as notified by the Government of India.
Source: the Income Tax Department and the annual Finance Act; deductions follow the Income-tax Act, 1961 (Sections 80C, 80D, 24(b), and others).
Loans & EMI
EMIs use the standard reducing-balance method that every Indian bank and NBFC follows:
EMI = P × r × (1 + r)ⁿ ÷ [ (1 + r)ⁿ − 1 ]where P = principal, r = monthly interest rate (annual ÷ 12 ÷ 100), and n = number of monthly instalments. Total interest is the sum of all EMIs minus the principal.
Rate context follows Reserve Bank of India norms.
Investments — SIP, FD, RD, PPF & more
SIPs use the future value of a monthly annuity; lump sums use standard compound interest:
FV = P × [ ((1 + i)ⁿ − 1) ÷ i ] × (1 + i)Scheme-specific tools follow each scheme's official rules — for example the PPF interest rate set quarterly by the Ministry of Finance under the small-savings scheme, and EPF/NPS rules from EPFO and the PFRDA. Returns shown are pre-tax estimates.
GST
We apply the GST rate slabs and the CGST/SGST/IGST split as notified by the GST Council.
Source: the Central Board of Indirect Taxes & Customs (CBIC).
Health & fitness
BMI is weight ÷ height² (kg/m²). For Indian users we flag the revised Asian-Indian thresholds (overweight at BMI ≥ 23, obese at ≥ 25) alongside the standard WHO bands, because the global cut-offs understate risk for South Asian body types. Calorie and BMR tools use the Mifflin–St Jeor equation, the current clinical standard.
Sources: the World Health Organization and the Indian Council of Medical Research (ICMR-NIN) / Ministry of Health & Family Welfare guidelines.
Math, date & everyday tools
Math tools (percentage, statistics, geometry, conversions) implement standard, textbook formulas. Date tools use the proleptic Gregorian calendar in Indian Standard Time (IST). Where a calculation has more than one accepted convention, the tool states which one it uses.
Accuracy & updates
Tax slabs, interest rates and scheme rules change — often at the annual Budget. When they do, we update the affected calculators and note it on the page. Our calculators are powerful aids, but for decisions that carry real money or health consequences we always recommend confirming the figure with a qualified professional. See our disclaimer for the full position.
Found something wrong?
Accuracy is the whole point, so we genuinely want to know if a number looks off. Tell us on our contact page and we'll check it against the source and fix it fast.