Free Online Calculators with the Math Shown
CalcSmith is a free online calculator website with 12 finance calculators — auto loan, mortgage, student loan, CD, PMI, credit card payoff, compound interest, retirement savings, home equity loan, car insurance, loan comparison and percentage calculators — that run instantly in your browser with no sign-up or account. Every calculator shows the formula it uses and a worked example, so each result can be checked by hand.
Browse finance calculators Percentage calculatorMost-used calculators
The finance core: borrowing, housing, debt and saving tools built around the questions people actually ask before signing anything.
Auto Loan Calculator
Monthly payment, total interest and amortization for any car loan.
🛡️Car Insurance Cost Estimator
Estimate your annual and monthly car insurance premium from the factors insurers actually use.
🎓Student Loan Calculator
Monthly payment, total interest and payoff date for student loans — plus the power of extra payments.
🏦CD Calculator
Maturity value, interest earned and APY for certificates of deposit at any rate and term.
🏠PMI Calculator
Monthly PMI cost, total PMI and the exact month it drops off your mortgage.
🏡Mortgage Calculator
Full monthly mortgage payment — principal, interest, tax, insurance and PMI — with amortization.
💳Credit Card Payoff Calculator
Months to debt-free and total interest for any card balance and payment.
📈Compound Interest Calculator
Final balance, contributions and growth for savings and investments over any horizon.
⚖️Loan Comparison Calculator
Compare up to three loan offers side by side on total cost, interest and payment.
🌅Retirement Savings Calculator
Project your retirement balance with contributions, employer match and compound growth.
🔑Home Equity Loan Calculator
Payment, total interest and combined loan-to-value for home equity loans.
％Percentage Calculator
Percent of a number, percentage share and percentage change — instantly.
Why the formula matters
A calculator that only prints a number teaches you nothing and can hide a bad deal. Every CalcSmith page shows the formula it uses, a worked example you can check by hand, and the parts of the result that lenders and salespeople prefer to leave blurry — total interest, total cost, and the date a fee like PMI finally disappears. If you can follow the math, you can negotiate with it.
Compare total cost, not payments
A lower monthly payment usually just means a longer, more expensive loan. Our comparison tool proves it with your own offers.
Know your PMI end date
Private mortgage insurance quietly costs thousands. See the exact month your balance reaches 80% and it can come off.
Escape minimum payments
Minimum payments are designed to keep you in debt for a decade. A fixed payment and a target date change everything.
How CalcSmith is different
Plenty of sites will compute a number for you; CalcSmith is built so you never have to trust one blindly. Every worked example on every page is recomputed by an automated test suite — 71 checks against independent calculations — before the site is published. If an example and its calculator ever disagree, the build fails and nothing ships. The person behind the site is on the author page.
Private by design
Every calculation happens in your browser. CalcSmith has no accounts, no sign-ups and no server receiving your financial figures — the numbers you type never leave your device. Close the tab and they are gone.
Frequently asked questions
Are CalcSmith calculators really free?
Yes — every tool is free, unlimited and requires no account or sign-up. The site is supported by advertising, and the calculators themselves run entirely in your browser.
How accurate are the results?
The calculators use the standard formulas lenders themselves use — amortized loan payments, compound growth, loan-to-value — and every page shows a worked example you can verify by hand. Results are still estimates: your lender's exact figures can differ slightly because of fees, exact day counts, and how your first payment date falls.
Is my financial data private?
Yes. All math runs locally in your browser using JavaScript. Nothing you type into a calculator is sent to or stored on a server — there is no database of user figures to leak.
Which calculator should I start with?
For a loan offer, the loan comparison tool shows which deal is truly cheapest. For a house purchase, start with the mortgage calculator, then check PMI. For debt, the credit card payoff calculator; for saving, the compound interest calculator. The finance hub groups them by job.