About CalcInterest

The calculators do the math in your browser

There are four tools here: the main compound interest calculator, a simple interest calculator, a savings calculator, and an investment calculator. Every one of them runs entirely on your device — the amounts you type are never sent to a server. There is no account to create, nothing to install, and nothing to pay.

Each result comes with a growth chart and a year-by-year table, because a single final number hides the most interesting part: when the growth happens. Deposit $7,500 at 5.5% compounded monthly and after 12 years you have about $14,489 — but the table shows that the last four years alone contribute more interest than the first five combined. That back-loaded curve is the whole story of compounding, and seeing it year by year is what makes it click.

Guides that show their arithmetic

The guidescover the ideas behind the calculator: how compounding works, why APR and APY differ, what the Rule of 72 does and does not tell you, and how the same force that grows savings inflates credit card debt. Every worked example in a guide is recomputed with the same formulas the calculators use, and where a claim depends on an outside fact — deposit insurance limits, inflation, historical returns — the guides point to official sources such as the SEC's Investor.gov, the FDIC, and the Consumer Financial Protection Bureau.

The person behind the site

I'm Luiz Torres, a software developer. I build small, free, client-side web tools, and CalcInterest is one of them — I wrote the calculator code, and I research and write every guide published here. You can find me on GitHub.

To be equally clear about what I am not: I am not a financial advisor, accountant, or licensed professional of any kind. My approach is that of an engineer — get the formulas right, verify every number, and cite official sources for anything I cannot compute myself.

Education only — not financial advice

Everything on this site, calculators and guides alike, is educational. It explains how the math of saving and investing works; it does not and cannot tell you what to do with your own money. Results are estimates that ignore taxes, fees, and changing rates. Before acting on anything you read or calculate here, talk to a qualified financial professional who knows your situation.

Corrections and feedback

If a number looks wrong or a sentence is misleading, I want to know. The contact page explains what to include, or email contact@calcinterest.com directly. How corrections are handled is documented on the editorial standards page.