FinTrex methodology

Formulas and assumptions

Stable mathematical formulas are maintained in application code. Editable assumptions—such as expected return, withdrawal rate, mortgage rate, inflation, fees, and time horizon—are kept separate so changing a default does not silently alter the underlying calculation method.

Annual-return convention

For investment and savings projections that calculate month by month, an entered annual return is treated as an effective annual return. FinTrex converts it to the equivalent monthly rate using (1 + annual return)^(1/12) - 1 before monthly compounding. This keeps a 7% annual assumption equal to 7% over one year before contributions or other cash flows.

Loan-rate convention

For fixed-rate amortising loans and mortgages, the entered annual interest rate is treated as a nominal annual rate with monthly periods, so the periodic rate is annual rate / 12. Payments use the standard amortising-loan formula unless the specific tool explicitly documents a different convention.

Contribution and fee timing

Monthly savings and investment contributions are generally modeled at month-end unless the calculator states otherwise. Annual asset-based investment fees are modeled using the documented simplified annual factor (1 + gross return) × (1 − fee), rather than by simply subtracting percentage points from a return. Dividend-reinvestment modelling identifies its assumed dividend timing so dividends are not credited with growth before they are modeled as reinvested.

Comparison tools

When FinTrex compares two strategies, the model aims to use an equivalent starting position, time horizon, and available cash-flow budget. Where one option has a lower modeled monthly cost, the comparison invests the difference rather than silently discarding it. Product taxes, transaction costs, insurance, and other omitted items are identified in the individual tool methodology.

Finite model horizons

Iterative goal and debt models use finite safety horizons. If the target remains unmet when the safety horizon is reached, the result is explicitly marked as beyond the model horizon; the horizon is not presented as a successful completion time.

Calculation presentation

Calculator pages show the user inputs, primary result, secondary results, a concise formula summary, limitations, calculation date, default-update date, and display currency where applicable. Detailed platform methodology is maintained on this page rather than repeated inside every calculator. Currency selection changes formatting only unless the tool is explicitly an exchange-rate scenario.

Time-sensitive data

Market and economic pages identify the provider and source where available. FinTrex's automated synchronization checks providers on schedules appropriate to the data and stores normalized observations for the interface. Publication frequency and observation period are kept distinct where required—for example, selected UK Labour Force Survey rates are rolling three-month estimates published monthly.

Failure handling

When an external source fails, FinTrex prefers the last verified value over an invented replacement, records or exposes failure state where appropriate, and retries automatically. A successful browser refresh does not imply that an official source has published a new observation.

External revisions

Official statistical agencies and market-data providers can revise previously published values. FinTrex therefore treats provider observations as sourced data rather than immutable facts and may change historical values after an official revision.

Corrections

Material formula, source, or presentation errors should be corrected promptly and regression-tested. A correction may involve changing application logic, updating an assumption, replacing a source, revising explanatory copy, or temporarily suppressing a result that cannot be supported reliably.