About HoldingCost

HoldingCost is a financial calculator platform. We build calculators that produce reliable numbers — calculators whose mathematics is open and whose outputs are reproducible. This page describes the engineering and editorial practices that produce the numbers you see on every page.

What we build

HoldingCost offers 78 calculators across 13 pillars — mortgage, property, loans, debt, vehicles, investments, business, logistics, comparison tools, optimisers, forecasts, personal finance, and education. Each calculator is paired with an editorial guide, a glossary of relevant terms, and a methodology disclosure that names the assumptions baked into the model. Embed-friendly variants of every calculator are available for use on third-party sites.

The platform is free to use. We do not require an account, we do not collect personally identifying information, and we do not sell user data. Calculator inputs live in your browser URL — sharing a URL shares the scenario verbatim, including in our embed variant.

How our calculators work

Each calculator's mathematics is implemented as a deterministic engine: a pure function that takes inputs and returns outputs without external state or hidden side effects. Engines are written in TypeScript with strict typing and use a decimal-arithmetic library — not native floating-point — for all financial values. The same inputs produce the same outputs every time, on every device.

Every engine result carries a reproducibility snapshot recording the engine version, the regulatory-schema version, and the assumption set that produced the number. When we update an engine — to fix a bug, refine a model, or reflect a regulatory change — the version bump means a prior shared scenario can be replayed against the original engine on request, and corrections to the math surface in the version history rather than disappearing into a silent rewrite.

For inputs that produce mathematically unreachable or degenerate results (a debt payment that doesn't cover interest, a savings rate that never reaches the goal, a break-even that never occurs), the calculator explains why and proposes a recoverable scenario rather than show "infinity", "NaN", or absurd numbers like a 200-year payoff. For inputs that are mathematically valid but unusual — an interest rate above 15%, a growth rate above 10% for long-term projections — the calculator surfaces an advisory warning so you can verify the input wasn't a typo.

Engineering practice

The mathematical engines are architecturally separated from the presentation layer. The same engine that renders results on a calculator page can be called from an embed iframe or, in future, from a server-side endpoint — and the answer is the same. Presentation code never reaches into the engine to override a number; engine code never reaches into the presentation layer to track a user. The separation is enforced at the package boundary so it cannot be bypassed by accident.

Every change to a calculator engine ships with a test suite covering the happy path, the boundary cases (zero values, minimum and maximum allowed inputs, near-degenerate inputs), and a precision-test suite that compares engine output against reference values computed independently from the underlying formula. Continuous integration runs an inventory of dedicated quality gates — type checking, lint, structural validation of every page's structured data, validation of trailing-slash and canonical-URL consistency, sitemap priority and lastmod correctness, build-output size budgets, accessibility, and end-to-end calculator workflows — on every change, and the build fails if any gate trips.

Content and methodology

Every calculator page surfaces its methodology and assumptions inline — what the model includes, what it excludes, and where the math diverges from real-world outcomes. Guides explain the underlying concepts in editorial form; glossary entries define the financial terms used across the calculators. Our editorial policy describes how content is researched, reviewed, dated for freshness, and corrected when readers spot errors.

Content is written to be globally neutral. We use generic currency placeholders ($X) and refer to "many jurisdictions" rather than naming specific countries. Tax rates, withholding rules, regulator thresholds, and consumer-credit caps differ by country and over time, and our generic calculators do not encode any of them. Where a real-world outcome depends on jurisdiction-specific rules, the methodology section on the calculator page says so explicitly. Always verify a number against the rules that apply where you live before relying on it — see the disclaimer for the full scope.

Accessibility and fairness

We design and build to WCAG 2.1 Level AA. The detail — including how to report issues — lives in our accessibility statement. Calculator results announce updates to assistive technologies; form fields carry visible labels and associated error messages; touch targets meet a minimum 44×44 px floor; focus indicators are visible and brand-coloured; and the colour palette is chosen for contrast compliance.

Advertising never influences our calculator results, defaults, rankings, or recommendations. The mathematics is open, versioned, and documented. Display advertising — when it is live — is served programmatically through Google AdSense, gated by user consent, and architecturally separated from the engine layer. See how we make money for the full revenue-model disclosure.

What we don't do

• We do not provide financial, legal, tax, or investment advice. Calculator outputs are estimates only; consult a qualified licensed professional in your jurisdiction.
• We do not sell, rent, or share personal data. The platform requires no account and collects no personally identifying information in normal operation. See our privacy policy for the full data flows.
• We do not take payment for content placement, calculator outputs, default values, rankings, or search positioning. No advertiser can pay to alter what our calculators output.
• We do not currently operate affiliate referrals, lead-capture forms, or sponsored placements. If that changes, the consent model will be re-prompted and our how-we-make-money page will reflect the new flows.

Operator information

HoldingCost is operated by TECH ASSURANCE PTY LTD (ACN: 661 252 320). For corrections, accessibility issues, or general enquiries, see our contact page. For privacy-related enquiries, see the contact in our privacy policy. For security disclosures, see our security policy.