About CompoundVision

What this is

CompoundVision is a suite of free financial calculators that run entirely in your browser. No file you load and no value you type is uploaded to a server — every calculation, conversion or transformation happens locally on your device, and the result is visible only to you. There is also an optional Pro tier for portfolio tracking; it is described under How it is funded below.

Why it exists

Most financial calculators online follow the same pattern: a slow page filled with intrusive ads, a paywall hiding the actually useful features, a forced signup, and an upload step that puts your data on someone else's server. After running into one too many of those, the operator (an independent developer based in Spain) started building self-contained alternatives one tool at a time. CompoundVision is the result for the financial category.

The design philosophy has stayed the same since the first commit: every tool must work without an account, without uploading anything sensitive, and without locking the obvious feature behind a "Pro" button. If a feature genuinely needs server-side computation, it is documented as such and the alternative is offered.

How it is funded

The free tier covers everything you can do in your browser without an account. The Pro tier (€7.99/month or €69.99/year) adds optional encrypted multi-device sync, live portfolio prices, DeFi/staking trackers, real-estate and expense tracking, tax tools and an ad-free experience. Pro is paid via Stripe; the free tier is paid for by display ads served by Google AdSense.

This means the site is sustainable without harvesting your data, gating tools behind a paywall, or pushing you toward a desktop app. If you find one of the tools genuinely useful and want to support continued development, the Buy Me a Coffee link in the footer is the most direct way.

Who is behind it

CompoundVision is built and maintained by Marco B., an independent developer based in Spain. The site is part of a small portfolio of utility web apps (CompoundVision for finance, AllYouNeed for general tools, JSONCraft for developers, OpenImages for image work, OpenPDF for PDFs, PingThat for networking). Each one shares the same private-by-default design.

If you would like to talk to a human about a tool, a bug or a feature you wish existed, the Contact page has a feedback form that lands in the operator's inbox within a few hours during EU working days.

How calculators are verified

Every calculator on the site is covered by an automated end-to-end test that runs on every deploy. The "Last verified — N calculators passing" line in the footer is set by CI, not hand-edited: it shows the date of the last green CI run and the exact number of calculators that passed. If a test breaks, the footer updates on the next build and the broken tool gets fixed before the count goes back to all-passing.

The full picture — how each formula is sourced, what disclaimers apply per tool, how foreign-currency conventions like TAE (Spain) vs APY (US) are handled — lives on the methodology page.

Sources we cite

Where a calculator implements a well-known formula or rule, the tool page cites the actual source rather than presenting it as something the site invented. A few examples:

• Compound interest — Bernoulli (1683) and Pacioli (1494) for the underlying math.
• FIRE / safe withdrawal rate — Bengen (1994) for the original 4% rule and the Trinity study (1998) for the historical-data update.
• Risk and return metrics — Markowitz (1952) for mean-variance and Sharpe (1966) for the Sharpe ratio.
• Portfolio allocation patterns — Bogle (Vanguard 1976) for index-fund three-fund variants and Dalio (All Weather 1996) for risk-parity.
• APY ↔ TAE — Truth in Savings Act (US, 1991) and BdE Circular 8/1990 (Spain) for the equivalent annual yield calculation in each jurisdiction.

The point is not to drop authoritative names. It is so you can verify the result against the original source if you want to, instead of taking a calculator's word for it.

Stack and openness

The site is built with Astro, Svelte 5 and Tailwind CSS 4, deployed on Cloudflare Pages, and uses no third-party trackers beyond aggregate Google Analytics 4 (with EU/UK consent gated to "denied" by default). Tool inputs never leave your browser, so there is nothing on a server to ask about under GDPR Article 15 — but if you want to know what we collect, the Privacy Policy spells it out fully.

Editorial independence

The advertising network (Google AdSense) does not influence which tools are built or how they work. There are no sponsored articles, no "best of" lists pushing affiliate links, no broker referrals, and no editorial choices made to favour an advertiser. If a tool exists on the site, it is because it was useful enough to the operator to build and ship it.

Not financial advice

The calculators on this site compute formulas. They do not give personalised financial advice, and the operator is not a licensed financial advisor in any jurisdiction. A number you see on /compound-interest or /fire-calculator is what the math says given your inputs — not a recommendation. Tax rules, currency conventions (TAE in Spain, APY in the US), and investment products vary across countries. For real-money decisions on a non-trivial scale, talk to a licensed advisor in your jurisdiction, or check the regulator in your country (CNMV in Spain, SEC/FINRA in the US, FCA in the UK).