How we build and check these calculators
Every calculator on CoinGarden runs on one tested, framework-agnostic math engine — the numbers you see come straight from code, never typed by hand. Automated tests check both the math and the writing before anything ships, every page is reviewed by a real person, and your inputs never leave your device.
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Every number comes from one tested engine
The math behind every calculator lives in a single, framework-agnostic engine written in plain TypeScript. It has no idea what a button or a chart is — it just takes your numbers and returns a result. We build it test-first: before a formula is written, we write the checks that describe what it should do (including a known-value or round-trip check), watch them fail, then write the code until they pass.
Nothing on a tool page is a hand-typed figure. When a page says "$200/mo at 7% for 30 years grows to about $244,000," that number came from the same engine that runs the Compound Interest Calculator live in your browser — so the worked example and the tool can never quietly disagree. The engine is covered by a growing suite of unit tests that run on every change.
We test the writing too, not just the math
Good numbers wrapped in drifting content still fail a reader. So we also run automated content checks that guard the things that matter for trust and for being found:
- Answer-first: every tool and guide opens with a short, plain-English answer you — or an AI assistant — can quote directly.
- Internal links intact: every page still links back into the learning path, so the site stays a connected whole instead of orphan pages.
- Consistent naming: the names of the tools and the learning path stay identical everywhere, so nothing reads as sloppily mass-produced.
- Real FAQ depth: every calculator ships a genuine set of questions and answers, not a token one-liner.
If a change breaks one of these, the test fails and the page doesn't ship until it's fixed.
We cite primary sources — and never fake them
Where a claim matters, we link the source, and we prefer the primary one: Investor.gov and the SEC, the IRS, the Federal Reserve, and fund providers such as Vanguard, rather than a summary of a summary. You'll find those links in the short trust note at the bottom of each tool.
Two things we will never do: invent star ratings or reviews the tools haven't earned, and dress up an estimate as a guarantee. Markets are uncertain; our job is to be honest about that, not to sell certainty.
A real person reviews every page
AI helps us draft and check, but it is a tool, not the author. Every page is read and approved by a real person — a learner-investor who uses these calculators to manage their own money — before it goes live. That's also why you won't find hundreds of thin, auto-generated pages here: we'd rather ship a few tools we'd actually use than flood the site. More about who's behind CoinGarden.
Your numbers stay on your device
The calculators run entirely in your browser. There's no signup, no account, and no server doing the math — so the figures you type never leave your device, and we never store them. You can plan with real, personal numbers without handing them to anyone. See our privacy policy for the details.
Educational, not financial advice
CoinGarden is here to help you build intuition and better money habits — it is not a financial adviser. Nothing here is a recommendation to buy, sell, or hold any investment, and every figure is an estimate based on the assumptions you provide. For decisions that affect your finances, talk to a qualified professional who knows your situation. If you're just getting started, the 30-day learning path is the best place to begin.