Calculation methodology

Last updated: 2026-08-18

Vicaya calculators are built as deterministic estimate tools. The result comes from the values entered on the page plus the formula and assumptions printed near the calculator. A changed input should produce a changed result for a clear reason.

Formula approach

Mortgage and loan calculators use standard amortization formulas where the payment is derived from principal, periodic rate, and number of periods. Payoff calculators then walk the balance period by period so extra principal, final payments, and remaining balances are based on a schedule rather than a shortcut.

Paycheck approach

U.S. paycheck pages estimate gross pay, federal withholding, FICA, deductions, and supported state or local rules using the inputs shown on the page. Payroll laws and withholding methods are simplified into calculator assumptions, so the result is an educational estimate, not payroll instruction.

Rounding

Calculations keep more precision internally than the screen shows. Displayed currency is rounded to the relevant minor unit, such as cents for U.S. dollars. A final schedule row may absorb a small difference so the balance reaches zero.

Charts

Donut and balance charts are generated only from real calculation output. A donut needs component parts, such as principal, interest, fees, tax, or insurance. A balance chart needs a schedule or projection, such as an amortization table or year-by-year investment balance.

India approach

India pages start from cost to company rather than gross salary, because that is the figure an offer letter states. From there the calculation separates the amounts that never reach a bank account — employer provident fund contribution and gratuity accrual — from the deductions that do come out of pay, being the employee provident fund share, professional tax set by the state, employee state insurance where wages fall under the threshold, and income tax deducted at source. Both tax regimes are computed on the same inputs so the comparison is like for like, including the Section 87A rebate and its marginal relief.

Testing

Each engine is exercised by test vectors held alongside it in the repository: fixed inputs with expected outputs, so a change that alters a result has to be deliberate rather than incidental. Several calculators share an engine, and regression vectors exist specifically to catch a change made for one page that moves the answer on another. Separate checks confirm that every registered route renders, that its controls carry labels, and that its layout holds at phone widths.

Confidence and unconfirmed rules

Some inputs are derived rather than entered, and some rules cannot be confirmed against a primary source. Where that is the case the result is labelled as such instead of being presented with the same confidence as a fully sourced figure. An Indian state whose professional tax schedule has not been verified against that state's own notification is reported as unconfirmed rather than being assigned a plausible number.

What a result is not

Where a page shows a verdict or a signal alongside a figure, that describes the tradeoff the entered numbers imply — a payoff that takes longer, a cost not recovered within the period entered. It is not an approval, a rejection, a recommendation, or a prediction, and no part of the site models a lender's actual underwriting.

For examples, use the mortgage amortization calculator, credit card payoff calculator, In-Hand Salary Calculator, or investment return calculator. The assumptions behind each are listed in sources and assumptions.