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Free online calculators for percentages, finance, health, time, and unit conversions. Fast results, no registration required.
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Sleep Hub
Bedtimes, sleep debt, jet lag, children's sleep — and the clinical work on chronic insomnia: CBT-I, sleep restriction, sleep diaries.
Homeowners
Measure a home job and work out what to buy: tile, gravel, mulch and concrete quantities, with the waste allowance and unit conversions that turn a plan into an order.
Free Online Calculators
Percentage Calculator
Calculate percentages, find what percent one number is of another, and more.
Percentage Change
Calculate percentage increase or decrease between two values.
GPA Calculator
Calculate your weighted and unweighted GPA from each course’s credits and grade.
VAT Calculator
Calculate VAT, net price, and gross price for any country.
Loan Calculator
Calculate monthly loan payments, total interest, and payoff schedule.
Mortgage Calculator
Calculate monthly mortgage payments including principal, interest, and taxes.
BMI Calculator
Calculate your Body Mass Index (BMI) and understand your weight category.
Target Heart Rate Calculator
Estimate your maximum heart rate and see your five training zones in bpm, using the percentage-of-HRmax or the Karvonen heart-rate-reserve method.
Macro Calculator
Turn a daily calorie target into grams of protein, carbohydrate and fat with a diet preset or a custom split.
BMR Calculator
Calculate your basal metabolic rate in kcal and kJ with the Mifflin-St Jeor, Harris-Benedict, Katch-McArdle and Schofield equations.
Calorie Calculator
Calculate your daily calorie target from your goal and pace, with the projected change over time and a macro split.
TDEE Calculator
Estimate your total daily energy expenditure, read the calories each activity level implies, and see the goal band around maintenance.
Body Fat Calculator
Estimate your body-fat percentage from tape measurements with the U.S. Navy method, or from BMI when you have no tape.
Height Calculator
Estimate a child’s adult height from both parents’ heights, or read a child’s height against the CDC growth reference at their age.
Age Calculator
Calculate your exact age in years, months, and days from your birth date.
Date Difference Calculator
Calculate the exact number of days, weeks, months, and years between two dates.
Days Until Date
Find out exactly how many days are left until any date.
Day Counter
Count the days between any two dates, past or future, with the inclusive or exclusive convention stated.
Unit Converter
Convert between units of length, weight, temperature, volume, speed, area, data, time, and transfer speeds.
Binary, Hex, Decimal and Octal Calculator
Convert a whole number between decimal, binary, octal and hexadecimal — all four shown at once — and add or subtract two exact integers in any of them.
Speed Calculator
Calculate average speed from distance and elapsed time, with metric and imperial units.
Currency Converter
Convert between 200+ currencies with live and historical exchange rates. Free, no registration required.
Salary Calculator
Calculate your net pay after tax for 7 countries. Convert between annual salary and hourly rate.
Tip Calculator
Calculate the perfect tip amount.
Discount Calculator
Calculate sale prices instantly.
Square Footage Calculator
Work out the square footage of a room or area, and the cost to cover it at a price per square foot.
Gravel Calculator
Estimate how much gravel an area needs at a given depth, in cubic yards, cubic feet and tonnes.
Tile Calculator
Find how many tiles and boxes an area needs, including the grout gap and a waste allowance.
Mulch Calculator
Work out how much mulch an area needs, in cubic yards, cubic feet and the number of bags.
Grade Calculator
Calculate your course grade from assignment weights, and the score a final exam needs for your target.
Area Calculator
Find the area of a rectangle, a triangle or a circle from its own measurements, in square metres, square feet and the unit you measured in.
Volume Calculator
Find the volume of a box, a cylinder or a sphere from its own measurements, in cubic metres, litres, cubic feet and US gallons.
Concrete Volume Calculator
Estimate concrete volume for slabs, rectangular columns and cylinders, then calculate bags from the stated package yield.
Surface Area Calculator
Find the surface area of a box, a closed cylinder or a sphere from its own measurements, in square metres, square feet and the unit you measured in.
Standard Deviation Calculator
Work out the standard deviation and the variance of a data set, with the population and the sample readings side by side.
Confidence Interval Calculator
Turn a sample mean, its standard deviation and the sample size into a 90, 95 or 99 percent confidence interval.
Z-Score Calculator
Turn a value, a mean and a standard deviation into a z-score, with the percentile and the tail probabilities beside it.
Percent Error Calculator
Find the percent error of a measurement against an accepted value, or the percent difference between two measurements.
Ratio Calculator
Simplify a ratio to its lowest terms, solve the missing term of a proportion, or scale a ratio by a factor.
Density Calculator
Find the density of a material from its mass and volume, or solve for the mass or the volume — with exact unit conversion and a sourced reference table of common substances.
Exponent Calculator
Raise a number to any power, or take any root — the answers are exact whenever the mathematics is, and the eight exponent rules stand beside the result.
Half-Life Calculator
Find how much of a quantity is left after a time, how long it takes to fall to a target, or the half-life itself between two readings — the decay relation, stated and derived.
Logarithm Calculator
Evaluate a logarithm, find the base it was taken in, or undo it and recover the argument — exact where the mathematics is exact, with the six log rules beside the result.
LCM Calculator
Find the least common multiple or the greatest common divisor of a list of whole numbers, exactly, with every number’s prime factorisation and the Euclidean working beside the result.
Ohm’s Law Calculator
Pick any two of voltage, current, resistance and power and the other two follow from V = I × R and P = V × I — exact where the numbers are exact, with the six relations beside the result.
Percent Off Calculator
Stack successive discounts on one price and see the final price, the saving and the effective single discount.
Random Number Generator
Draw random numbers from a range you set, with or without repeats, and repeat the same random draw with a seed.
Scientific Notation Converter
Convert ordinary or scientific notation to normalized scientific notation and an expanded decimal, including zero and negative values.
Auto Loan Calculator
Calculate your monthly car payment.
Compound Interest Calculator
Calculate how your savings grow with compound interest.
Transfer and Stamp Duty Calculator
Estimate buy-stage transfer or stamp duty for the UK, Italy, France, Germany, Ontario, New South Wales and California, from official published rates.
Notary and Closing Costs Calculator
Estimate French notary fees and transfer tax for a purchase, then add your own agency and bank fees to get the total closing cost against the price.
Present Value Calculator
Find the present value or future value of money — the time value of money.
Debt Payoff Calculator
Calculate how fast you can pay off your credit card or loan debt.
ROI Calculator
Work out the return on an investment: the net gain or loss, the ROI, and the annualised ROI when a period is given.
XIRR Calculator
Find the annualized return implied by dated positive and negative cash flows, with multiple-root and search-limit disclosures.
Commission Calculator
Calculate a sales commission on a flat or tiered rate, then split it between the producer and the house.
Sale Net Proceeds Calculator
Calculate the cash you keep at closing: sale price less agent fee, notary and sale costs, and the mortgage balance.
Simple Interest Calculator
Calculate simple interest without compounding from principal, annual rate and time in years.
Sleep Calculator
Find the best time to wake up or go to bed using sleep cycle science.
Sleep Restriction Therapy Calculator
Calculate your sleep window using sleep restriction therapy (SRT) and CBT-I principles.
Sleep Debt Calculator
Calculate your total sleep debt and find out how long recovery takes.
Chronotype Calculator
Find your chronotype and estimate social jet lag based on your sleep schedule.
Jet Lag Calculator
Plan your sleep schedule for time zone travel and reduce jet lag.
Kids Sleep Calculator
Find age-based sleep recommendations for children and teenagers.
Ideal Weight Calculator
Calculate your ideal weight with the Devine, Robinson, Miller, Hamwi, Peterson and Broca formulas, and see the healthy weight range for your height.
Lean Body Mass Calculator
Estimate your lean body mass and fat mass from your weight and body-fat percentage, read the fat-free mass index against reference values, and compare the Boer, James and Hume estimates.
One Rep Max Calculator
Estimate your one-rep max from a weight and the reps you lifted, with Epley, Brzycki and Lombardi side by side.
Pace Calculator
Work out running or cycling pace, time or distance from the other two values.
Army Body Fat Calculator
Check the U.S. Army waist-to-height standard and see the superseded 2023 tape estimate.
Caffeine Cutoff Calculator
See how much of a caffeine dose is left in the body at bedtime, the latest time you can have it and stay at or below the level you choose, and the hour it falls to that level.
Nap Calculator
Work out how long to nap and when to wake: a power nap, or one to three full sleep cycles of about 90 minutes each.
VAT vs Sales Tax
Learn the key differences between VAT and sales tax.
Fixed vs Variable Rate
Understand fixed vs variable mortgage rates.
APR vs Interest Rate
Learn the difference between APR and nominal interest rate.
Gross vs Net Pay
Understand the difference between gross and net pay.
EURIBOR & Mortgages
How EURIBOR affects mortgage payments.
Usury Rate (France)
Understanding the French usury rate for mortgages.
SCHUFA & Credit Score
How SCHUFA affects your loan applications in Germany.
Italian First-Home Mortgage
Italy's first-home mortgage benefits for under 36.
Home Remodel Material Quantities
How much material a home remodel or upkeep job needs: measure, add a waste allowance, convert to the purchase unit and order.
What Is CBT-I?
Learn what Cognitive Behavioral Therapy for Insomnia (CBT-I) is, its core components, and why it is the first-line treatment for chronic insomnia.
Sleep Restriction Therapy Explained
How sleep restriction therapy works for insomnia: time in bed, sleep efficiency, fixed wake time, safety floors, and weekly adjustments.
Sleep Diary and Sleep Efficiency
How to track your sleep with a sleep diary and calculate sleep efficiency for CBT-I sleep restriction therapy.
Stimulus Control Therapy
How stimulus control therapy strengthens the bed-sleep connection and helps treat chronic insomnia.
Sleep Compression vs Sleep Restriction
The difference between sleep compression and sleep restriction therapy, and when a gradual approach may be more appropriate.
CBT-I vs Sleep Hygiene
Why CBT-I is more effective than sleep hygiene alone for chronic insomnia, and how both approaches differ.
Cognitive Techniques for Insomnia
Cognitive restructuring techniques from CBT-I: managing worry time, catastrophic thoughts, and sleep performance anxiety.
When Sleep Restriction May Not Be Appropriate
Medical and safety considerations before trying sleep restriction therapy: bipolar disorder, seizure risk, sleep apnea, and other contraindications.
How to Adjust Your Sleep Window Week by Week
How to adjust your sleep window each week based on sleep efficiency during CBT-I sleep restriction therapy.
CBT-I Plan: How the Pieces Fit Together
How sleep diary, stimulus control, sleep restriction, cognitive techniques, and relaxation fit into a structured CBT-I program.
Sleep Debt Recovery
Learn how sleep debt works, how to estimate your shortfall, and how to recover with gradual pacing.
Chronotype and Circadian Rhythm
Understand chronotypes, circadian rhythm, social jet lag, and how schedule alignment affects sleep quality.
Jet Lag Sleep Planning
Plan your sleep for time zone travel with light exposure guidelines and gradual schedule shifts.
Kids Sleep Needs by Age
Age-based sleep recommendations for children and teens, including naps and individual variation.
Sleep Cycles and Stages
Understand the sleep cycle, REM and deep sleep stages, and how cycle timing affects sleep quality.
Light and Melatonin Timing
How daily light timing works around your own clock, and where melatonin fits as the body's dark signal.
About CalclyHub
Learn what CalclyHub does, how our calculators work, and where estimates should be independently verified.
Editorial Policy
How CalclyHub writes, reviews, updates, and corrects calculator content.
Sources and Methodology
How CalclyHub chooses formulas, default values, tax references, health references, and update checks.
Time Duration Calculator
Calculate elapsed hours and minutes between two clock times, including overnight shifts.