Are my financial numbers uploaded to a server?

No. CalcTools is 100% client-side. Every calculation — mortgage, loan, compound interest, tax — runs in your browser as plain JavaScript. There is no backend and no /api route. The site's Content-Security-Policy (connect-src 'self') even restricts which hosts the page may contact, so the privacy guarantee is enforced by the browser itself.

Are the calculations accurate?

Yes — each calculator uses the standard, published formula for its problem (the loan PMT formula, compound-interest future value, marginal tax bands, the HKMA stress-test rule, and so on). The verify suite hand-checks reference values against the implemented math before every build. Still, these are decision aids, not financial advice; confirm with a professional for a binding decision.

How is the currency converter's exchange rate sourced?

The converter ships with a build-time snapshot of exchange rates (taken from a public, no-key exchange-rate API at build time) bundled same-origin — it never makes a runtime request to any server in this MVP build. So currency conversion works offline and exposes no browsing data to a third party.

Do the Hong Kong calculators reflect the current year?

They use the published 2024/25 HK rates: Salaries Tax progressive bands (2%/6%/10%/14%/17%) and 15% standard rate with a $132,000 basic allowance; property Stamp Duty on the smoothed ad valorem band scale; MPF at 5% employee + 5% employer capped at the $30,000 monthly relevant-income limit. Always confirm the current figures on gov.hk before relying on a number for a real filing or purchase.

Does it work offline?

Yes. After the first load the app shell is cached, so every calculator works with no internet connection. Install CalcTools as a PWA and it opens and runs offline.

Business

ROI & Payback Calculator

Return on investment, annualized return, and simple payback period for any project.

ROI & Payback Calculator

Return on investment, annualized return (CAGR), and a simple payback period.

Initial investment

Final value

Years held

yrs

Annual cash inflow

Your numbers never leave your device — all math runs in your browser.

Result

Return on investment

50.00%

Gain: $5,000.00

Annualized (CAGR)14.47%

ROI = (final − initial)/initial. Annualized return is the compound annual growth rate. Payback ignores the time value of money.

Printable PDF report, saved scenarios & compare are Pro features.

One-time unlock, no subscription. Unlock CalcTools Pro →

How to use this calculator

Enter the initial investment and the final value.
Set the number of years held (for the annualized return).
Optionally add an annual cash inflow to see the payback period.

Bookmark ROI & Payback Calculator — it works offline once loaded. Figures are decision aids, not financial advice.