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).
Compound Interest Calculator
Future value, interest earned and APY from any compounding frequency.
Simple Interest Calculator
Interest and total from principal, rate and time (I = P·r·t).
Inflation Calculator
Future cost and lost buying power of money at any inflation rate.
Debt-to-Income Calculator
Your DTI ratio from monthly debts and income, with lender limits.
Home Affordability Calculator
The home price you can afford under the 28/36 lending rule.
Savings Goal Calculator
The monthly deposit needed to reach a target by your deadline.
APR Calculator
The true annual percentage rate of a loan once fees are included.
Amortization Schedule Calculator
A full payment table of principal, interest and balance, with CSV.
Mortgage Payoff Calculator
See how extra payments shorten your loan and the interest you save.
Debt Snowball Calculator
Smallest-balance-first payoff order, debt-free date and total interest.
Debt Avalanche Calculator
Highest-APR-first order that pays the least total interest.
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.
Break-Even Calculator
Units and revenue to break even, with contribution margin and profit.
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).
BMR Calculator
Calories your body burns at rest, via the Mifflin-St Jeor equation.
TDEE Calculator
Total daily energy expenditure and your maintenance calories.
Calorie Calculator
Daily calories to lose, maintain or gain weight from your goal.
Running Pace Calculator
Solve pace, time or distance, with race splits and speed.
Weighted GPA Calculator
Weighted GPA on the 5.0 scale with honors and AP/IB bonuses.
Ideal Weight Calculator
Ideal body weight by the Devine, Robinson and Miller formulas.
Calories Burned Calculator
Calories burned by activity, weight and time using MET values.
Macro Calculator
Daily protein, carb and fat grams from your calorie target.
Pregnancy Due Date Calculator
Estimated due date and gestational age from your last period.
Ovulation Calculator
Your ovulation day and fertile window from your cycle.
One-Rep Max Calculator
Estimate your 1RM from reps, with a percentage training table.
Calorie Deficit Calculator
Daily calories and deficit to lose weight by a target date.
Heart Rate Zone Calculator
Max heart rate and five training zones from your age.
Body Surface Area Calculator
BSA in m² by Mosteller, Du Bois, Haycock and Gehan-George.
Waist-to-Hip Ratio Calculator
Your WHR and the WHO health-risk band for your sex.
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.
Tip & Split Calculator
Tip, grand total and what each person owes when splitting a bill.
Gas Mileage Calculator
MPG, L/100km and the fuel cost of any trip.
Unit Converter
Length, weight, temperature, volume, area and speed in any units.
Password Generator
Strong, random passwords built securely in your browser.
Scientific Calculator
Trig, logs, powers, roots and constants in degrees or radians.
Fraction Calculator
Add, subtract, multiply or divide fractions in lowest terms.
Ratio Calculator
Simplify a ratio or solve A:B = C:D for the missing value.
Standard Deviation Calculator
Sample and population standard deviation, variance and mean.
Mean, Median, Mode Calculator
Average, median, mode, range, sum and count from any list.
Area Calculator
Area of a rectangle, circle, triangle, trapezoid or parallelogram.
Volume Calculator
Volume of a box, cylinder, sphere, cone or pyramid.
Scientific Notation Calculator
Convert any number to and from scientific notation (a × 10ⁿ).
Quadratic Equation Solver
Solve ax² + bx + c = 0 with roots, discriminant and vertex.
Slope Calculator
Slope, line equation, angle, distance and midpoint from two points.
Prime Number Checker
Is it prime? See factors, prime factorization and nearest primes.
GCD & LCM Calculator
Greatest common divisor and least common multiple of any numbers.
Permutation & Combination Calculator
Compute nPr and nCr from n and r, with factorials and formulas.
Percentage Increase / Decrease Calculator
Apply a percent rise or fall, or find the change between two values.
Factorial Calculator
Compute n! exactly with big-integer precision and the steps.
Logarithm Calculator
log base 10, ln, log base 2 and any custom base, with change of base.
Concrete Calculator
Cubic yards, bag counts and cost for a slab or footing.
Paint Calculator
Paintable area and how many gallons your walls need.
JSON Formatter
Beautify, minify and validate JSON with clear error messages.
Base64 Encoder / Decoder
Encode text to Base64 and decode it back, with full Unicode.
URL Encoder / Decoder
Percent-encode and decode URLs and query-string values.
Hash Generator
SHA-256, SHA-1, SHA-384 and SHA-512 hashes of any text.
QR Code Generator
Turn any URL or text into a QR code and download it as PNG.
UUID Generator
Generate one or many random version-4 UUIDs (GUIDs).
Color Picker
Pick a color and copy its HEX, RGB and HSL codes.
HEX to RGB Converter
Convert hex color codes to RGB and HSL, and back.
Unix Timestamp Converter
Convert epoch time to a date in UTC and local time, and back.
CSV to JSON Converter
Turn CSV or spreadsheet data into a clean JSON array.
Binary Calculator
Add, subtract, multiply or divide binary, with decimal and hex.
Hex to Decimal Converter
Convert hexadecimal to decimal and binary, and back again.
IP Subnet Calculator
Subnet mask, network, broadcast and host range from IP and CIDR.
Random Number Generator
Pick random numbers in any range, unique or with repeats.
Dice Roller
Roll d4–d20 virtual dice with a modifier for games and RPGs.
Password Strength Checker
A password's entropy in bits and an estimated time to crack it.
Regex Tester
Test regular expressions with live highlighting and groups.
JWT Decoder
Decode a JSON Web Token's header and payload claims.
Markdown to HTML
Convert Markdown to clean HTML with a live preview.
HTML Entity Encoder
Escape special characters to HTML entities and back.
Cron Expression Generator
Build a crontab schedule and explain any cron expression.
Image to Base64
Turn any image into a Base64 data URI for CSS and HTML.
Binary to Text Converter
Decode binary to text and encode text to binary, with Unicode.
YAML to JSON Converter
Convert YAML to clean, formatted JSON — mappings, lists and nesting.
SQL Formatter
Beautify SQL with clean indentation and uppercased keywords.
XML Formatter
Beautify or minify XML with clean indentation, validated as you go.
CSS Minifier
Strip comments and whitespace from CSS with a byte-saving readout.
JavaScript Minifier
Minify JS by removing comments and whitespace, strings kept safe.
HTML Minifier
Collapse inter-tag whitespace and comments; pre and script preserved.
Base64 to Image Decoder
Paste a Base64 data URI to preview and download the image.
Epoch to Human Date Converter
Turn a Unix timestamp into a readable UTC and local date, or back.
Word Counter
Words, characters, sentences and reading time as you type.
Character Counter
Characters with and without spaces, with platform limits.
Case Converter
UPPER, lower, Title, Sentence, camel, snake and kebab case.
Slug Generator
Turn any title into a clean, URL-friendly slug.
Lorem Ipsum Generator
Placeholder text by paragraphs, sentences or words.
Text Diff Checker
Compare two texts and highlight what changed, line by line.
Roman Numeral Converter
Convert numbers to Roman numerals and back (1–3999).
Number to Words
Spell any number in English words and cheque currency form.
Morse Code Translator
Convert text to Morse code and back, with audio playback.
Random Name Generator
Generate random first, last or full names for any use.
Random Quote Generator
Get a random inspirational quote with its author.
Text Repeater
Repeat any text many times with custom separators.
Reading Time Calculator
How long any text takes to read - slow, average, fast and aloud.
Words Per Minute Calculator
Your typing, reading or speaking WPM, with accuracy-adjusted net WPM.
Color Palette Generator
Build harmonious color schemes from one base color.
CSS Gradient Generator
Create linear and radial gradients and copy the CSS.
Box Shadow Generator
Design a CSS box-shadow with a live preview and copy it.
Color Contrast Checker
WCAG contrast ratio with AA/AAA pass-fail and a live preview.
Image Resizer
Resize images by pixels or percent, keep the ratio, download - no upload.
Image Cropper
Crop an image to an exact pixel rectangle and download it.
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.