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.

Savings

Compound Interest Calculator

See how compound interest grows a lump sum with regular contributions over time.

Compound Interest Calculator

How a lump sum plus regular monthly contributions grows with compound interest.

Starting amount

Monthly add

Return rate

%/yr

Years

yrs

Compounds / year

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

Result

Final balance

$54,713.58

You contributed$34,000.00

Interest earned$20,713.58

Future value of a lump sum plus an ordinary annuity. Assumes a steady return rate; real returns vary.

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

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

How to use this calculator

Enter your starting amount and a monthly contribution.
Set the expected annual return rate and the number of years.
Set how often interest compounds (12 = monthly). Read your final balance and interest earned.

Bookmark Compound Interest Calculator — it works offline once loaded. Figures are decision aids, not financial advice.