Free calculators
Calculators that show their work.
20 free tools for car buying, mortgages, loans, saving, health and everyday math. Every one runs in your browser, explains the formula underneath, and lets you copy a link with your numbers in it. No ads, no sign-up, nothing you type is sent anywhere.
Car buying
The numbers a dealership runs on its screen, run on yours first.
Home & mortgage
What a house really costs each month, how much house fits your income, and what extra payments do.
Mortgage Calculator
Full monthly payment with taxes, insurance, PMI and HOA, the payoff schedule, and what extra payments save.
Open the calculator →House Affordability Calculator
How much house your income and debts support, using the 28/36 rule lenders use.
Open the calculator →Amortization Calculator
Every payment of any loan, split into principal and interest, with extra payments and the interest they save.
Open the calculator →Loans, saving & investing
Loans, credit cards, compound growth, retirement and the return on money you put to work.
Loan Calculator
Solve for the payment, the loan amount, the term or the interest rate — whichever you don't know.
Open the calculator →Compound Interest Calculator
What a starting amount plus monthly deposits grows into, year by year, at any rate and compounding frequency.
Open the calculator →Retirement Calculator
Are you on track? Projected savings at retirement vs. what the income you want will actually require.
Open the calculator →ROI Calculator
Return on an investment — total and annualized — or the real return on a marketing campaign after costs and margin.
Open the calculator →Credit Card Payoff Calculator
How long a balance takes to clear at a given payment, or the payment that clears it by a date — and what it costs in interest.
Open the calculator →Salary Calculator
Convert pay between hourly, daily, weekly, biweekly, monthly and yearly, with or without unpaid days off.
Open the calculator →Health & fitness
The standard formulas clinicians and trainers use, explained plainly.
BMI Calculator
Body mass index with the adult categories, your healthy weight range, and how far you are from it.
Open the calculator →Calorie Calculator
Daily calories to maintain, lose or gain weight from your BMR and activity level, with a simple macro split.
Open the calculator →Body Fat Calculator
Body fat percentage from a tape measure using the U.S. Navy method, with lean mass and a second estimate from BMI.
Open the calculator →Everyday math
Percentages, tips, dates, ages and grades, done right the first time.
Sales Tax Calculator
Add tax to a price, back it out of a receipt total, or find the rate you were charged.
Open the calculator →Percentage Calculator
What is X% of Y, X is what percent of Y, percent change, and increase or decrease a number by a percent.
Open the calculator →Tip Calculator
Tip and total, split any number of ways, with one-tap presets and round-up.
Open the calculator →Age Calculator
Exact age in years, months and days, total days alive, the weekday you were born, and your next birthday.
Open the calculator →Date Calculator
Days between two dates (with business days), or add and subtract years, months, weeks and days from a date.
Open the calculator →GPA Calculator
Semester GPA from grades and credits, your new cumulative GPA, and the average you need to hit a target.
Open the calculator →No calculator matches that. Try a different word, or tell us what you need and we may build it.
These calculators give estimates for planning and education. They are not financial, tax, legal or medical advice, and the lender, dealer, tax authority or clinician's figures govern. See the terms of use.
Need a calculator your customers would use?
Dealerships, lenders, contractors, clinics and gyms all have a question customers ask before they buy. Slickrock builds the tool that answers it on your site, branded to you, and wires it to your lead flow.