Why MiniCalc
looks the way it does.

The philosophy

Calculator sites tend to be black boxes covered in ads. You type numbers in, a result appears, you take it on faith. We think a calculator should also teach — show the formula, work the example, explain why the answer is what it is. That way you can spot when a result looks off, and you can use the calculator again without it.

Accuracy

Every engine here is written as pure JavaScript with documented formulas. Where they exist, we test against canonical textbook examples — e.g., the compound interest engine matches $1,000 at 5% compounded monthly for 10 years ≈ $1,647.01. Where there's ambiguity (annuity-due vs annuity-ordinary, tip on pre-tax vs post-tax, BMI category boundaries), we document the choice on the calculator's page.

We cross-check headline financial calculators (mortgage, compound interest, loan) against Bankrate and NerdWallet to the penny on standard scenarios. If you find a discrepancy, it's a bug — please tell us.

Where the formulas come from

• Mortgage / loan — standard fully-amortizing fixed-rate formula M = P·r(1+r)ⁿ / ((1+r)ⁿ − 1).
• Compound interest — A = P(1 + r/n)ⁿᵗ with periodic contributions added at the end of each compounding period.
• BMI — WHO categories. Adult cutoffs; not appropriate for children or highly athletic builds.
• Age — calendar-correct years/months/days, walking the calendar (not 365.25-day averaging).
• Percentage / tip — basic arithmetic with the working shown on each page.

Speed

MiniCalc is a static site. There's no backend, no server-side rendering, no framework runtime. Each calculator widget is plain HTML + CSS + a few KB of JavaScript that includes the engine and a tiny chart loader. We deliberately avoid React, Vue, Tailwind's runtime, or any tracking pixel. The result is sub-1-second first-load on most connections.

Privacy

We don't track you. There's no analytics SDK, no advertising script, no cookie banner because we don't set cookies. Your inputs live in the URL (so you can share a result link) and optionally in your browser's localStorage (so your theme preferences persist) — both stay on your machine. No data leaves your device when you use a calculator.

The webfonts and the chart library load from a public CDN; your browser fetches them directly. We never see those requests.

Why your URL matters

Every modal and every calculator page mirrors its inputs to the URL. That means:

• Bookmark a specific result and you'll see the same numbers next visit.
• Share the URL and the recipient sees your inputs and result, not a generic page.
• Refresh in the middle of a calculation — your inputs survive.

When results differ

Results depend on assumptions. The most common reasons MiniCalc will disagree with another calculator:

• Compounding period — daily vs monthly vs continuous yields slightly different numbers.
• Contribution timing — beginning vs end of period.
• Rounding — bankers' rounding vs half-up, and at which step rounding is applied.
• Inclusions — mortgage tools that include or exclude PMI, taxes, insurance, HOA.