CPM Calculator
Work out cost per 1,000 impressions, total ad spend, or reach for any budget.
PayPal Fee Calculator
See the exact PayPal fee and what actually lands in your account.
eBay Fee Calculator
Estimate eBay final-value fees and your real take-home per sale.
Percentage Calculator
Percent of a number, percentage change, and X is what % of Y.
Investment Calculator
Project compound growth with regular contributions over any horizon.
Loan Calculator
Monthly payment, total interest and a full amortization schedule.
NPV Calculator
Discount future cash flows to today and judge a project at a glance.
Sales Tax Calculator
Add or back out US sales tax at any rate, forward or reverse.
Mortgage Calculator
Monthly principal-and-interest payment and a full amortization schedule.
Car Payment Calculator
Monthly auto-loan payment from price, down payment, tax, APR and term.
Credit Card Payoff Calculator
How many months to clear a balance, and the total interest you'll pay.
401(k) Calculator
Project your 401(k) at retirement, employer match included.
Retirement Calculator
Project savings vs the nest egg your income goal really needs.
ROI Calculator
Return on investment, net profit and annualized ROI (CAGR).
Profit Margin Calculator
Gross profit, margin and the equivalent markup from revenue and cost.
Markup Calculator
Set a selling price from cost and a markup, and see the resulting margin.
Discount Calculator
Sale price and savings from a percent-off, including stacked discounts.
Paycheck Calculator
Estimate US take-home pay after federal tax, Social Security and Medicare.
Time Card Calculator
Add daily clock-in/out times into weekly hours and gross pay.
Hours Calculator
Duration between two times, in hours-and-minutes and decimal hours.
GPA Calculator
Compute a weighted GPA on the standard US 4.0 scale by credit hours.
Grade Calculator
Weighted course grade and letter grade from assignment scores.
BMI Calculator
Body mass index and weight category, in metric or US units.
Body Fat Calculator
Estimate body fat percentage with the US Navy tape method.
BAC Calculator
Estimate blood alcohol content with the Widmark formula (educational).
Percentage Change Calculator
Percent increase or decrease between an old and a new value.
Tip Calculator
Gratuity, grand total and the per-person share when splitting a bill.
Age Calculator
Your exact age in years, months and days, plus days lived.
Date Difference Calculator
Days, weeks and months between two dates, business days optional.
Square Footage Calculator
Area in square feet and the material cost per square foot.
Why Calcool is different
Most “free calculator” sites give you a box, a button and a number — and leave you guessing whether the answer is right or how it was reached. Calcool was built on the opposite idea: every tool is auditable. Under each calculator you'll find the precise formula it applies, a fully worked example with real numbers, an FAQ that answers the questions people actually search for, and links to the authoritative source the method comes from — the IRS, the SSA, the U.S. Department of Transportation, accounting standards bodies and similar.
The calculators run entirely in your browser. Nothing you type is uploaded, stored or shared — the math happens on your device the instant you click Calculate. That makes Calcool quick on any connection and private by default.
New tools are added regularly. If you'd like to see a calculator that isn't here yet, the contact details are on the about page.