About FinCalculate

What this site is for

FinCalculate publishes free calculators for the money decisions most people actually face: what a mortgage really costs each month, how long a card balance takes to clear, whether a balance transfer beats its fee, and whether a spare dollar does more against a debt than in an account.

Some of those questions have a dollar answer and some have a threshold. Paying a debt down is a guaranteed return equal to its interest rate, so the useful output is often not a figure but a bar an alternative has to clear. Where that is the case, the calculator solves for the bar rather than picking a number and hoping it holds.

There are a great many financial calculators on the web and most of them give you a number with no provenance: no formula, no assumptions, no date, no source. The gap this site is trying to fill is not another payment figure but a defensible one, the same answer, with everything behind it visible, so you can tell whether it applies to you.

How the calculators are built

The arithmetic lives in a single engine shared by every calculator on the site, covered by unit tests that assert exact figures rather than approximate ones. Money is handled in whole cents throughout and only converted to dollars for display, so a 360-month schedule cannot accumulate floating-point drift.

Where a result can be checked against a closed-form answer, it is. The mortgage calculator's breakeven rate, for instance, must equal the mortgage rate exactly when no tax applies on either side, because paying down a mortgage is a guaranteed return equal to its interest rate. Several such identities are asserted in the test suite, which is a stronger guarantee than a model that is merely self-consistent.

The comparison standard

Every comparison on this site holds two things fixed: the monthly amount of cash spent, and the date on which both scenarios are measured. This matters more than it sounds. A plan that clears a debt early frees up money, and if a model stops measuring at that point, or quietly forgets to invest the freed-up payment, it credits one path for finishing sooner while ignoring what the other path was doing in the meantime. That single omission is the most common flaw in payoff calculators, and it consistently favours paying down early.

Who writes this

FinCalculate is built and maintained by Acun Özdilek. It is an independent site, not a lender, broker, adviser or affiliate of one, and no calculator here is sponsored, placed or adjusted at anyone's request. It carries advertising, which is what pays for it; the ads are chosen by Google and are not endorsements. See the terms of use.

Rather than ask you to take a stranger's credentials on faith, the site is built so you do not have to. Every formula is written out on the page. Every assumption is listed, including the unflattering ones. Every tax rule links to the IRS or CFPB document it came from, so you can check it against the source rather than against us. The arithmetic engine is covered by tests that assert exact figures and closed-form identities, several of which can be derived on paper. That is a stronger claim than a byline, and it is one you can verify.

Editorial standards

• Every calculator states the formulas it uses, in full, on the page rather than in a footnote.
• Every assumption is listed explicitly, including the ones that make a result more conservative than reality and the ones that make it less.
• Tax treatment is kept deliberately simple. Where a rule is complicated or depends on circumstances we do not ask about, we say what we assumed instead of guessing.
• Sources are linked to primary documents, IRS publications rather than summaries of them.
• Each calculator carries the date it was last reviewed.
• Nothing here is personalised advice, and no page recommends a course of action. The output is a comparison; the decision is yours.

What the models do not do

These calculators compare expected values. They assume steady returns, unchanging tax rates and constant payments, none of which describe real life. In particular, paying down a debt is a certain return while an investment return is not, and no chart on this site captures that difference in risk. A breakeven of 6% does not mean a 7% expected return is the better choice, it means it is the better bet, which is a different claim. Liquidity matters too: money in a brokerage account can be reached in a way that home equity generally cannot.

Corrections

If you think a calculation is wrong, please say so, write to hello@fincalculate.info with the inputs you used and the figure you expected. Modelling errors get fixed and the page's last-updated date changes when they are. In a subject where a wrong formula could cost someone real money, we would rather be corrected than trusted.

See also the full disclaimer, our terms of use and our privacy policy.