Free Online Calculators
Fast, accurate calculators for finance, health, math and everyday life. No sign-up, no downloads — every tool runs instantly in your browser, with formulas explained and sources cited.
What is SlickCalcs?
SlickCalcs is a free library of online calculators for everyday decisions: figuring out your paycheck, planning a loan, tracking calories, or solving a math problem. Every calculator is built for regular people — no finance degree or math background needed. Type in your numbers, get a clear answer in plain English, and see exactly how the math works.
Who is it for? Anyone in the US (and beyond) who wants a quick, trustworthy number: employees checking their take-home pay, families budgeting a mortgage, students doing homework, or anyone comparing prices, tips, and savings. If you've ever Googled "how much will I..." — this site is for you.
Why trust the answers? Each tool shows its formula, a worked example with real numbers, and the authoritative source it comes from (the IRS, peer-reviewed research, standards bodies). Our math is covered by automated tests, and every page shows when it was last reviewed. Learn more about how we verify our calculators →
Finance Calculators
View all →Paycheck Calculator
See exactly what lands in your bank account each payday — after federal tax, FICA, and state tax.
Refinance Break-Even Calculator
See how many months of lower payments it takes to recover your closing costs — and whether refinancing is actually worth it.
Pay Raise Calculator
See exactly what that raise means — your new salary, the extra per paycheck, and the hourly equivalent.
Salary to Hourly Calculator
Convert salary to hourly (or hourly to salary) in seconds — adjusted for your actual hours, not just the standard 40.
HYSA Calculator
See how fast your savings grow in a high-yield account — with monthly contributions and real compounding.
Compound Interest Calculator
Watch your money grow — project compound growth with monthly deposits, any rate, and any timeframe.
Daily Compound Interest Calculator
See what daily compounding does for your savings — with monthly deposits and a side-by-side monthly comparison.
Tip Calculator
Calculate the tip, split the bill, and see what each person owes — in seconds.
Discount Calculator
Find the real sale price in seconds — including stacked discounts stores hope you won't calculate.
Sales Tax Calculator
Add sales tax or VAT to any price — or work backwards from the total to the pre-tax price.
Currency Converter
Convert between world currencies with live mid-market rates — plus the honest truth about fees.
Health Calculators
View all →TDEE Calculator
Discover how many calories you burn per day — and what to eat to lose, maintain, or gain weight.
Body Fat Calculator
Find your estimated body fat percentage with just a tape measure — plus your fat mass, lean mass, and fitness category.
Protein Intake Calculator
How much protein do you really need? Get a research-backed daily target for your weight and goal — plus a simple per-meal breakdown.
BMR Calculator
Your body burns calories even doing nothing. Find your Basal Metabolic Rate — the foundation of every calorie plan.
Macro Calculator
Turn your calorie target into daily protein, carbs, and fat grams — pick a proven split or dial in your own.
Water Intake Calculator
Forget the "8 glasses" myth — get a hydration target matched to your weight, your activity, and your climate.
Ideal Weight Calculator
See the classic clinical weight formulas side by side — Devine, Robinson, Miller — plus your healthy BMI range.
Due Date Calculator
When will your baby arrive? Get an estimated due date from your last period or conception date — plus how far along you are today.
Heart Rate Zones Calculator
Stop guessing your effort — get your 5 heart rate training zones from your age, personalized with your resting heart rate.
Pace Calculator
Pace, time, distance — know any two, get the third instantly. Works in kilometers and miles.
Math Calculators
View all →Percentage Calculator
Find any percentage in seconds — what X% of a number is, percent change between two values, and more.
Average Calculator
Mean, median and mode side by side — plus weighted averages, sorted data, and a quick visual chart.
Fraction Calculator
Add, subtract, multiply, divide and simplify fractions — with every step shown, plus mixed numbers and decimals.
Ratio Calculator
Simplify ratios, solve proportions, and scale recipes or plans to any size — ratio, decimal and percent together.
Scientific Calculator
A full scientific calculator in your browser — trig, logs, exponents, fractions and equation solving, with keyboard-first input.
Standard Deviation Calculator
Find standard deviation and variance for any dataset — population or sample — with every step shown.
Everyday Calculators
View all →Cooking Converter
Convert cups to grams, ounces to milliliters, and scale any recipe up or down — with per-ingredient weights.
Fuel Cost Calculator
Estimate any trip's fuel cost from distance, fuel efficiency and gas price — plus cost per mile and per person.
Time Calculators
View all →Age Calculator
Your exact age in years, months and days — plus total days lived, your birth weekday, zodiac signs, and next-birthday countdown.
Date Duration Calculator
Count days, weeks and months between any two dates — or count down to an event, with an optional business-days mode.
Hours Calculator
Add up work hours, build a weekly timesheet, or find the time between two clock readings — in HH:MM and decimal hours.
Time Calculator
Add and subtract time, measure durations between two times, and convert between seconds, minutes, hours, days and weeks.
Time Zone Converter
Convert time across world zones instantly — with daylight saving handled and a meeting planner for US, EU and Asia.
Education Calculators
View all →GPA Calculator
Find your semester and cumulative GPA in seconds — unweighted or weighted, high school or college.
Grade Calculator
Find out exactly what you need on the final — or compute your weighted grade across categories.
Converters Calculators
View all →Celsius to Fahrenheit Converter
Convert °C to °F (and back) instantly — with the formula, everyday reference points, and a quick chart.
Cm to Inches Converter
Convert centimeters to inches (and back) instantly — with the formula, a quick chart, and feet+inches breakdown.
Kg to Lbs Converter
Convert kilograms to pounds (and back) instantly — with the formula, a quick chart, and stone breakdown for UK readers.
Unit Converter
Convert length, weight, temperature, volume and speed instantly — metric to imperial made easy.
Why SlickCalcs?
- Instant answers. Every calculator works the moment the page loads — results are computed on our servers first, then update live as you type.
- Transparent math. We show the exact formula, a worked example with real numbers, and the source it comes from.
- Built for mobile. Over 70% of calculator searches happen on phones — our tools are designed thumb-first and load in under a second.
- Free forever. No accounts, no paywalls, no spam. Supported by unobtrusive advertising.