We publish our math so you can check our work. Here's how each calculator computes its answer, and where we source the defaults.
Loan / EMI calculators
Reducing-balance EMI formula (RBI standard):
EMI = P × r × (1+r)^n / ((1+r)^n − 1)
where P = principal, r = monthly rate (annual ÷ 12 ÷ 100), n = tenure in months. Amortisation schedule splits each EMI into interest (balance × r) and principal (EMI − interest).
FD / RD calculators
FD compounds quarterly (Indian banking standard): A = P × (1 + r/4)^(4t). RD uses the standard annuity formula for monthly contributions with quarterly compounding.
SIP / Lumpsum / Mutual Fund
Future value of SIP: FV = PMT × (((1+r)^n − 1) / r) × (1+r), assuming investment at month-start. Lumpsum: FV = P × (1+r)^n.
XIRR
Newton-Raphson iteration on the XNPV equation. Converges to < 1e-7 within typical 30 iterations. Matches Excel XIRR to 4 decimal places on test cases.
Income tax
Both old and new regime slabs for FY 2025-26 (AY 2026-27), as per Finance Act 2024. Standard deduction ₹75K (new regime), ₹50K (old). Cess 4% on tax. Rebate under Sec 87A: up to ₹25K on new regime, ₹12.5K on old, per current rules.
PPF, EPF, NPS, NSC
Interest rates as notified by the Ministry of Finance each quarter. Defaults:
- PPF: 7.1% (Q4 FY 25-26)
- EPF: 8.25% (FY 24-25)
- NSC: 7.7% (current tranche)
- NPS: equity/corporate-debt/G-sec allocation as per user input
Insurance cover (Term, HLV, Health)
Term cover: Maximum of (15× annual income), DIME method, and Human Life Value at 7% discount, 6% growth, 30% self-consumption.
HLV: Sum of (Income × (1 − self%) × (1+growth)^t) / (1+discount)^(t+1) from t = 0 to retirement.
Health cover: Base sum insured by city tier × age multiplier × family-size multiplier, projected at 12% medical inflation. Base values derived from IRDAI claim data and insurer rate cards:
- Tier 1 (metros): ₹10L base
- Tier 2: ₹7L base
- Tier 3: ₹5L base
Where our defaults come from
- FD / RD / savings rates: sampled from SBI, HDFC Bank, ICICI Bank and small finance banks.
- Term / health premium estimates: online portals of HDFC Life, Max Life, ICICI Prudential, TATA AIA, HDFC ERGO, Care Health.
- Tax slabs: Income Tax Department notifications for the current FY.
- Inflation / returns: long-term averages - equity 12%, debt 6.5%, inflation 6%, medical inflation 12%.
Limitations we are honest about
- Rates change - we aim to refresh defaults quarterly but they can drift.
- Our insurance calculators ignore your specific health history, which insurers weight heavily.
- SIP/lumpsum projections assume constant returns. Real markets don't.
- Tax calculators assume you're not eligible for special rebates (disability, senior citizen) unless explicitly coded.
Correction log
- 22 Apr 2026: Added insurance calculators (Term, HLV, Health, Policy Ladder, FD Ladder). Launched guides section.
- Apr 2025 baseline: Original calculators shipped.