Methodology

Loan & EMI calculators

Formula: Reducing-balance EMI = P × r × (1+r)ⁿ / ((1+r)ⁿ − 1)

Source: RBI Master Direction on Interest Rate on Advances (DBR.Dir.BC.No.14/13.03.00/2015-16). All major Indian banks (SBI, HDFC Bank, ICICI Bank, Axis Bank, Kotak Mahindra) use this method as of 1 October 2019 when the External Benchmark Lending Rate (EBLR) regime became mandatory for floating-rate retail loans.

Verification: Output is cross-checked against published EMI calculators from SBI, HDFC Bank, Groww, and ClearTax. Values match within ₹50-100 (rounding only).

SIP & investment calculators

SIP formula: FV = P × ((1 + r)ⁿ − 1) / r × (1 + r), where r is monthly rate and n is months.

Compound interest: A = P × (1 + r/n)^n×twith n compoundings per year over t years. Quarterly compounding (n=4) is the Indian bank default for FDs.

XIRR: Newton-Raphson iteration on the IRR equation for irregular cash flows — same method Excel and Google Sheets use.

Return assumptions: Where the calculator suggests a default expected return (e.g. 12% for equity SIP), the figure is sourced from NIFTY 50 TRI 15-year CAGR data published by NSE Indices. Past returns are not future guarantees; calculators stress-test at 10% (conservative) and 14% (aggressive) where the UI exposes the rate field.

Indian tax calculators

Income tax:Slabs, surcharge tiers, and rebates are implemented from the latest Finance Act (FY 2024-25 onwards). New regime: ₹0-3L nil, ₹3-7L 5%, ₹7-10L 10%, ₹10-12L 15%, ₹12-15L 20%, >₹15L 30%. Surcharge at 10% / 15% / 25% above ₹50L / ₹1cr / ₹2cr taxable income. 4% health and education cess on tax plus surcharge. Section 87A rebate makes tax zero up to ₹7L taxable in new regime.

Capital gains: Implements post-July 2024 rates per Finance Act 2024. Equity STCG 20%, equity LTCG 12.5% above ₹1.25L annual exemption per FY. Property/gold LTCG 12.5% without indexation (with transitional 20%-with-indexation option for pre-23-Jul-2024 acquisitions). Debt MFs purchased on/after 1 April 2023 always taxed at slab.

GST: Five slabs (0%, 5%, 12%, 18%, 28%) plus additional cess on luxury/sin items. Forward calculation: Net + GST = Gross. Reverse: Net = Gross × 100 / (100 + Rate).

Stamp duty:State-by-state rates sourced from each state's revenue/registration department circular. Female-owner concessions captured where applicable (Delhi 4% vs 6%, Haryana 5% vs 7%, etc.). Verified against state portals every 6 months.

PPF, EPF, NPS, and government schemes

PPF: Government-notified rate (currently 7.1%); calculator field accepts any rate so it stays accurate after each quarterly revision. Annual compounding on the lower of monthly minimum balance (between 5th and last day) — standard PPF rule per scheme circular.

EPF: 12% employee + 12% employer (of which 8.33% goes to EPS up to ₹15K salary, rest to EPF). Annual interest at government-notified rate (currently 8.25%). Calculator models annual increment and salary-cap rules.

NPS: Market-linked returns based on chosen pension fund manager and asset allocation. Default expectation: 75%-equity Aggressive scheme has delivered ~10-11% blended over 10-15 year windows historically. At 60: 60% lump sum tax-free, 40% mandatory annuity (taxable). Annuity rate assumed at ~6.5% — adjust if your specific annuity quote differs.

Health & fitness calculators

BMI: kg / (m × m). WHO cut-offs (18.5, 25, 30). For South Asian populations we note the tighter healthy range (18.5-22.9) recommended by some Indian clinical guidelines.

BMR: Mifflin-St Jeor equation (Mifflin et al., American Journal of Clinical Nutrition, 1990) — the most accurate predictive equation against indirect calorimetry per American Dietetic Association evaluation.

Body fat percentage: US Navy circumference method using neck, waist, and (for women) hip. Tracks within ±3-4% of DEXA scan results for tracking changes.

Pregnancy:Naegele's rule (LMP + 280 days) for due date. Standard obstetric convention; clinical ultrasound dating in first trimester is more accurate (within ±5 days) and should always be preferred where available.

Construction & material calculators

Concrete: Wet volume × 1.54 dry conversion factor. Mix ratios per IS 10262 — M15 (1:2:4), M20 (1:1.5:3), M25 (1:1:2). Cement bag = 50 kg = 0.0347 m³.

Steel weight: Per IS 1786, weight per metre = D² / 162 where D is diameter in mm. So 12mm bar = 0.889 kg/m.

Brick: Standard 19×9×9 cm brick, ~8 bricks per cubic foot of wall accounting for 10mm mortar joints.

Currency and number formatting

All currency outputs use the Indian numbering convention (lakh and crore separators: 1,23,45,678). Where calculations involve large numbers, we display lakh/crore breakdowns alongside the absolute rupee figure for readability.

Where you can verify

Each calculator's “References” section links to the originating authority — RBI Master Directions for loans, IT Department's bare Act for tax, the published clinical paper for health formulas. If you find a discrepancy between our calculator and the originating source, please email leomultimediaofficial@gmail.com with the URL and the divergence — we'll investigate and correct within 5 working days.