Calculation methodology
How CalcMantra turns your inputs into estimates — and what we do not claim.
Last updated 2026-09-18
Where the math runs
Calculator logic runs in your browser using the same TypeScript math modules that power the site. Results are not sent to a bank API. Each tool page shows the formula, a worked example, and assumptions so you can verify the approach.
EMI and reducing-balance loans
Standard EMI uses EMI = P × r × (1 + r)^n / ((1 + r)^n − 1), where r is the monthly rate and n is months. Prepayment tools apply extra amounts to principal and recompute the schedule under the mode described on the page (typically keep EMI, cut tenure).
SIP and investment projections
SIP and lumpsum tools compound at the annual expected return you enter, converted to a periodic rate. Markets do not move in a straight line — treat corpora as planning ranges, not guarantees.
Tax and statutory tools
Income tax, GST, TDS, HRA, gratuity, and similar tools use configuration modules keyed to a financial year or rate window (for example FY 2026-27). When a page lists sources, those are the references we used. Official portals and notifications always win if they differ.
Rounding
Displayed INR amounts are typically rounded to the nearest rupee for readability. Intermediate steps may keep more precision. Lenders and payroll systems may round differently.
Review cadence
We review tax-year and small-savings assumptions when rules change and note a content-reviewed date on the site. If something looks outdated, tell us via the Contact page with the URL and what changed.
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