About FinCalc

FinCalc is a set of free financial calculators built and maintained by one person — me. No company, no investors, no email capture. Just the tools I wanted to exist when I was trying to work out my own numbers.

Who I am

I'm Sastihari S, a software engineer & builder based in Tamil Nadu, India. I build web applications and automation systems for a living, and I write software that has to be correct — which is exactly the mindset a financial calculator needs.

I want to be clear about what I am and am not: I'm an engineer, not a licensed financial adviser, accountant or mortgage broker. What I can promise is that the mathematics on this site is correct, published and tested. What I can't do is tell you what you personally should do with your money — that's a conversation for a professional who knows your full situation.

Why I built it

Every time I looked up a financial number online, I ran into the same three problems:

• Half-answers. Mortgage calculators showing principal and interest while ignoring taxes, insurance and PMI — the difference between the number you plan for and the number you pay.
• Email walls. Tools that made you hand over contact details to see a result, then sold that to lenders.
• Black boxes. No explanation of how anything was computed, so you couldn't tell whether the result was even right.

So this site has three rules, and I hold them without exception.

The rules

1. Show the whole number. Property taxes, PMI, origination fees, sales tax, inflation — the uncomfortable parts are included by default, not hidden behind an "advanced" toggle.
2. Publish the formula. Every calculator shows the mathematics it uses, right on the page. If you can't verify a tool, you're just trusting a stranger with your money decisions.
3. Ask nothing of you. No sign-up, no email, no account. Everything runs in your own browser — the numbers you type never leave your device and are never sent to a server.

How the math is verified

Every calculation lives in a tested code module. The test suite checks results against independently known correct values from standard finance references — not against my own implementation, which would only prove the code agrees with itself.

It also includes round-trip tests: for example, the calculator solves for the monthly payment needed to clear a debt in 24 months, then feeds that payment back into the payoff calculator and checks it lands on exactly 24. Amortization schedules are verified to sum precisely to the original loan amount with a final balance of exactly zero — the kind of rounding bug that leaves competitors' tables a few dollars off.

There are currently 11 calculators covering mortgages, loans, debt payoff, savings, investing and retirement, with more being added.

Found a mistake?

Tell me and I'll fix it. Genuinely — a wrong number on a finance site is the worst thing that can happen here, and I'd rather be corrected than trusted blindly. You can reach me on the contact page.