About Financial Calculator

Financial Calculator is an indie project by jugo_dev, a software developer who built these tools for personal use and decided to make them public so everyone can make better financial decisions.

The project was born out of a genuine need: finding accurate, fast, ad-free financial calculators that worked directly in the browser. There wasn't exactly what I needed, so I built it. I use them daily and I hope they're just as useful to you.

Important notice: this is not financial advice

The calculators on this site are educational and informational tools. The results they show are mathematical estimates based on the data you enter. They do not constitute financial, tax, investment or legal advice. Before making any significant financial decision, consult a certified financial advisor who knows your specific situation.

Methodology and calculation accuracy

Most calculators on the internet use native JavaScript arithmetic, which accumulates rounding errors in decimals. On this site, all calculations use Decimal.js, an arbitrary-precision decimal arithmetic library that eliminates this problem.

Compound interest

A = P × (1 + r/n)^(n×t) + PMT × [((1 + r/n)^(n×t) - 1) / (r/n)]

A = Final balance
P = Initial principal
r = Annual interest rate (decimal)
n = Compounding periods per year
t = Time in years
PMT = Periodic contribution

This is the standard financial mathematics formula for the future value of an annuity combined with the growth of the initial principal. The formula is the same used in finance textbooks and Excel/Google Sheets spreadsheets.

Loan amortization (French method)

Payment = P × [r(1+r)^n] / [(1+r)^n - 1]

P = Loan principal
r = Monthly interest rate (annual nominal rate / 12)
n = Total number of payments

The French amortization method is the most common for mortgages and personal loans. Each payment is constant; early payments are mostly interest while later payments are mostly principal. The loan simulator generates the full amortization schedule payment by payment, allowing you to simulate early repayments and see their impact on the outstanding balance.

The source code for all calculations is available in the project repository for anyone who wants to audit it.

Privacy and data

This site does not collect any personal data. All calculations run directly in your browser; no number you enter ever leaves your device. We only use localStorage to save form values between sessions so you don't have to re-enter them every time. That data stays exclusively on your device.

No tracking cookies, no third-party analytics, no advertising. You can read the full privacy policy.

Support the project

If these tools have been useful to you, you can support the project by buying me a coffee. Every bit helps keep the site running and improving.

Support on Ko-fi

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