Donaldson R F Free Online Calculators
Calculators for money, health, maths, time, building, tax and everyday planning. Type in your numbers and get the answer straight away.
162 free tools in this category. No sign-up, no limits.
Percentage Calculator
Three common percentage calculations in one place.
Open tool →Unit Converter
Convert length, weight, and temperature between units.
Open tool →Currency Converter
Convert between world currencies using live exchange rates.
Open tool →BMI Calculator
Estimate Body Mass Index from height and weight.
Open tool →Age Calculator
Find your exact age in years, months, and days.
Open tool →Date Difference Calculator
Find the days, weeks, and months between two dates.
Open tool →Tip Calculator
Work out the tip and split the bill between people.
Open tool →Discount Calculator
Find the sale price and how much you save.
Open tool →Compound Interest Calculator
See how an amount grows over time with compound interest.
Open tool →Simple Interest Calculator
Calculate interest that doesn't compound.
Open tool →Loan Payoff Calculator
See how long it takes to pay off a loan.
Open tool →Salary to Hourly Calculator
Convert between annual salary and hourly rate.
Open tool →Savings Goal Calculator
Find out how much to save monthly to reach a goal.
Open tool →Car Loan Calculator
Estimate your monthly car loan payment.
Open tool →Overtime & Time and a Half Calculator
Calculate overtime pay and time-and-a-half rates.
Open tool →Days Until Calculator
Find out how many days are left until a date.
Open tool →Decimal to Fraction Converter
Convert a decimal into a simplified fraction.
Open tool →Roman Numeral Converter
Convert between numbers and Roman numerals.
Open tool →Final Grade Calculator
Find the score you need on your final exam.
Open tool →Cooking Measurement Converter
Convert cups, grams, ounces, tablespoons, and more.
Open tool →BMR Calculator
Estimate your Basal Metabolic Rate.
Open tool →Ideal Weight Calculator
Estimate ideal body weight using clinical formulas.
Open tool →Ovulation Calculator
Estimate your fertile window and ovulation date.
Open tool →Period Calculator
Predict your next few periods based on your cycle.
Open tool →Business Days Calculator
Count the weekdays between two dates.
Open tool →Date Calculator
Add or subtract time from a date.
Open tool →Hours Calculator
Add up hours and minutes worked.
Open tool →Zodiac Sign Finder
Find your zodiac sign from a birth date.
Open tool →Number Base Converter
Convert numbers between decimal, binary, octal, and hex.
Open tool →Number to Words
Convert a number into its written-out English words.
Open tool →Rule of Three Calculator
Solve simple proportions instantly.
Open tool →Fraction Calculator
Add, subtract, multiply, or divide fractions.
Open tool →Square Root Calculator
Find the square root of any positive number.
Open tool →Exponent Calculator
Calculate a base number raised to a power.
Open tool →Circumference Calculator
Find a circle's circumference, area, and diameter.
Open tool →Slope Calculator
Find the slope of a line between two points.
Open tool →Pythagorean Theorem Calculator
Find the missing side of a right triangle.
Open tool →Sales Tax Calculator
Calculate sales tax and the final price of a purchase.
Open tool →Significant Figures Calculator
Round a number to a chosen number of significant figures.
Open tool →Pregnancy Due Date Calculator
Estimate a pregnancy due date and gestational age.
Open tool →Moon Phase
See the moon phase for any date.
Open tool →Day of the Year
See which day of the year a date falls on.
Open tool →Week Number Calculator
Find the ISO week number for any date.
Open tool →Current Season Finder
Find out what season a date falls in.
Open tool →Gasoline vs Ethanol Calculator
Find out which fuel is the better value for a flex-fuel car.
Open tool →Fuel Cost Calculator
Estimate the fuel cost for a trip.
Open tool →Calendar Generator
Generate and print a calendar for any month and year.
Open tool →Event Countdown
Create a live countdown to any date and time.
Open tool →Savings Simulator
See how much you'll have saving a fixed amount monthly.
Open tool →Time to a Million Calculator
Find out how long it takes to save your first million.
Open tool →Financing Simulator
Simulate financing for a vehicle, property, or any purchase.
Open tool →GPA Calculator
Calculate your Grade Point Average on a 4.0 scale.
Open tool →Log Calculator
Calculate logarithms in any base.
Open tool →Scientific Notation Converter
Convert a number to and from scientific notation.
Open tool →Square Footage Calculator
Calculate room area and estimate material cost.
Open tool →P-Value Calculator
Calculate a p-value from a Z-score.
Open tool →Confidence Interval Calculator
Calculate a confidence interval for a sample mean.
Open tool →Mortgage Calculator
Estimate your monthly mortgage payment including tax and insurance.
Open tool →Debt Payoff Calculator
Compare the Snowball and Avalanche methods to pay off debts.
Open tool →Retirement Calculator
Estimate your retirement savings.
Open tool →Inflation Calculator
See how much an amount of money is worth over time.
Open tool →ROI Calculator
Calculate return on investment and annualized return.
Open tool →Mean, Median, Mode Calculator
Calculate mean, median, mode, and range of a data set.
Open tool →Standard Deviation Calculator
Calculate standard deviation and variance.
Open tool →Permutation & Combination Calculator
Calculate nPr and nCr.
Open tool →GCD & LCM Calculator
Calculate the greatest common divisor and least common multiple.
Open tool →Quadratic Equation Solver
Solve ax² + bx + c = 0.
Open tool →TDEE Calculator
Calculate your Total Daily Energy Expenditure.
Open tool →Macro Calculator
Calculate daily protein, carb, and fat targets.
Open tool →Heart Rate Zone Calculator
Calculate your training heart rate zones.
Open tool →Time Zone Converter
Convert a specific date and time between time zones.
Open tool →Leap Year Checker
Check whether a year is a leap year.
Open tool →Age Difference Calculator
Calculate the age difference between two people.
Open tool →Recipe Scaler
Scale a recipe's ingredients for a different number of servings.
Open tool →Coffee Ratio Calculator
Calculate the right coffee-to-water ratio for your brew.
Open tool →Race Time Predictor
Predict your finish time at a new distance.
Open tool →Bowling Score Calculator
Calculate your ten-pin bowling score frame by frame.
Open tool →Golf Handicap Calculator
Estimate a golf handicap index from recent scores.
Open tool →Net Worth Calculator
Calculate your net worth from assets and liabilities.
Open tool →Emergency Fund Calculator
Calculate how big your emergency fund should be.
Open tool →Freelance Hourly Rate Calculator
Calculate the hourly rate you need to hit your income goal.
Open tool →Ratio & Proportion Calculator
Simplify a ratio or solve a proportion.
Open tool →Triangle Solver
Solve a triangle's missing angles and area from its sides.
Open tool →Surface Area & Volume Calculator
Calculate surface area and volume of common 3D shapes.
Open tool →Prime Number Checker
Check if a number is prime, and list primes in a range.
Open tool →Waist-to-Hip Ratio Calculator
Calculate your waist-to-hip ratio.
Open tool →One Rep Max Calculator
Estimate your one-rep max for weightlifting.
Open tool →Water Intake Calculator
Calculate your recommended daily water intake.
Open tool →Weekday Finder
Find what day of the week any date falls on.
Open tool →Customer Lifetime Value (LTV) Calculator
Estimate how much a customer is worth over time.
Open tool →Customer Acquisition Cost (CAC) Calculator
Calculate how much it costs to acquire a customer.
Open tool →Churn Rate Calculator
Calculate customer churn and retention rate.
Open tool →Depreciation Calculator
Calculate straight-line depreciation of any asset.
Open tool →Markup vs Margin Calculator
See markup and margin side by side from cost and price.
Open tool →Matrix Calculator
Add, multiply, and find determinants of matrices.
Open tool →Probability Calculator
Calculate the probability of combined independent events.
Open tool →Sleep Cycle Calculator
Find the best time to sleep or wake up based on 90-minute cycles.
Open tool →Fibonacci Sequence Generator
Generate the Fibonacci sequence up to N terms.
Open tool →Perfect Number Checker
Check if a number is a perfect number.
Open tool →Armstrong Number Checker
Check if a number is an Armstrong (narcissistic) number.
Open tool →Shift Schedule Calculator
Calculate total hours worked across multiple shifts.
Open tool →Business Hours Difference Calculator
Calculate working hours between two dates, excluding weekends.
Open tool →Marathon Pace Calculator
Calculate the pace you need for a race goal time.
Open tool →Swimming Pace Calculator
Calculate swimming pace per 100m and predict other distances.
Open tool →Ohm's Law Calculator
Calculate voltage, current, resistance, or power.
Open tool →Resistor Color Code Calculator
Calculate resistor value from color bands.
Open tool →Amortization Schedule Calculator
Month-by-month loan schedule with interest, principal and balance. Add extra payments.
Open tool →VAT & GST Calculator
Add VAT or GST to a price, or remove it from a tax-inclusive total.
Open tool →APR Calculator
Find the true annual percentage rate of a loan once fees are included.
Open tool →Marketplace Fee Calculator
Fees, payout and profit on eBay, Amazon, Etsy, PayPal or Stripe sales, plus the price for your margin.
Open tool →Payment Processing Fee Calculator
Work out a card processor's fee and the net amount you'll receive, with editable Stripe/PayPal UK example rates.
Open tool →Z-Score Calculator
Calculate a z-score with percentile and tail probabilities, or convert a z-score to a value.
Open tool →T-Score Calculator
Convert raw scores or z-scores to T-scores (mean 50, SD 10) and back.
Open tool →Factorial Calculator
Calculate n! exactly for large numbers, with digit count and trailing zeros.
Open tool →Child Growth Percentile Calculator
Height and weight percentiles by age and sex using WHO and CDC growth data (informational).
Open tool →Pregnancy Weight Gain Calculator
Recommended weight gain in pregnancy from your BMI, using IOM / National Academies guidelines.
Open tool →Meeting Planner Across Time Zones
Compare cities side by side and find a meeting time that works for everyone.
Open tool →Date Format Converter
Convert dates between DD/MM/YYYY, MM/DD/YYYY, ISO 8601 and written formats.
Open tool →Party Food Portion Calculator
How much pizza, meat, rice and sides to prepare per guest for a party or event.
Open tool →Barcode Check Digit Calculator
Calculate or verify the check digit of EAN-13, UPC-A, EAN-8, GTIN-14 and SSCC-18 codes.
Open tool →Dimensional Weight Calculator
Find a parcel's volumetric and chargeable weight from its size and actual weight.
Open tool →Wholesale & Retail Price Calculator
Go from factory cost to wholesale and retail price with margin, markup and VAT.
Open tool →Unit Price Comparator
Compare pack sizes and multipacks to see which is the best value per kg, litre or item.
Open tool →Scientific Calculator
Brackets, powers, roots, trigonometry, logarithms, factorials and memory.
Open tool →Speed, Distance & Time Calculator
Find speed, distance or time from the other two values.
Open tool →Bill Splitter
Split a bill equally or by item, with tip and a simple settle-up.
Open tool →Stamp Duty Calculator (UK)
Estimate residential Stamp Duty Land Tax in England and Northern Ireland, for home movers, first-time buyers and additional homes.
Open tool →UK Take-Home Pay Calculator
Estimate your UK take-home pay for 2026/27 after income tax, National Insurance, pension and student loan.
Open tool →Student Loan Repayment Calculator
Work out your monthly UK student loan repayment for Plans 1, 2, 4, 5 and postgraduate loans, and how long it may take to clear.
Open tool →HMRC Mileage Allowance Calculator
Calculate the HMRC approved mileage allowance for cars, vans, motorcycles and bikes, and the tax relief if your employer pays less.
Open tool →Alcohol Units Calculator
Count the UK alcohol units in pints, glasses of wine and spirits, and compare your week with the 14-unit guideline.
Open tool →Body Fat Calculator
Estimate body fat percentage from tape measurements (US Navy method) or BMI, in cm and kg or inches and stones.
Open tool →Calories Burned Calculator
Estimate the calories you burn walking, running, cycling, swimming and 25 other activities from your weight and time, using MET values.
Open tool →CAGR Calculator
Work out the Compound Annual Growth Rate (CAGR) between a starting and ending value over any number of years, or project a future value from it.
Open tool →Break-Even Calculator
Work out how many units you need to sell, and at what revenue, to cover your fixed and variable costs and reach break-even.
Open tool →Power Converter (HP, kW, CV)
Convert power between kilowatts, mechanical horsepower (hp), metric horsepower (CV/PS), electrical horsepower and BTU/h, using exact definitions.
Open tool →Inventory Turnover Calculator
Work out inventory turnover ratio and days to sell stock, from cost of goods sold and average inventory value over a period.
Open tool →Wind Chill & Dew Point Calculator
Calculate wind chill (feels-like temperature) from air temperature and wind speed, and dew point from temperature and humidity.
Open tool →Screen PPI Calculator
Calculate a screen's pixels per inch (PPI) from resolution and diagonal size, plus dot pitch, physical size and aspect ratio.
Open tool →Download Time Calculator
Work out how long a download or upload takes from the file size and your internet speed in Mbps, with overhead and a table of speeds.
Open tool →Cake Tin Converter
Convert a cake recipe between round, square and rectangular tins in cm: multiplier by area and volume, plus equivalent tin sizes.
Open tool →Cost in Work Hours Calculator
Turn any price into hours and days of work from your own take-home pay, for one-off buys and monthly bills. No tax estimate.
Open tool →Technology Age Calculator
See how long ago a technology milestone was, from a small sourced list of standards, software, devices and space missions.
Open tool →UK Tax Code Decoder
Decode a UK PAYE tax code: what the numbers and letters mean, Scottish (S) and Welsh (C) prefixes, emergency codes and K codes.
Open tool →Pre-Decimal Currency (£sd) Converter
Convert old British money (pounds, shillings and pence) to decimal pounds and back, plus a reference table of farthings, florins, crowns and guineas.
Open tool →UK Notice Period Calculator
Work out the UK statutory minimum notice period for an employee or employer, based on length of service under the Employment Rights Act 1996.
Open tool →National Living Wage & Minimum Wage Checker
Check UK hourly pay against the National Living Wage and National Minimum Wage rates by age band, including the apprentice rate.
Open tool →UK National Insurance Calculator
Work out UK National Insurance for 2026/27: Class 1 for employees (and employer NI), or Class 2 and Class 4 for the self-employed.
Open tool →UK Dividend Tax Calculator
Work out UK tax on dividend income for 2026/27, after the £500 dividend allowance, using the basic, higher and additional dividend tax rates.
Open tool →UK Capital Gains Tax Calculator
Work out UK Capital Gains Tax for 2026/27 after your £3,000 annual exempt amount, including Business Asset Disposal Relief.
Open tool →Statutory Redundancy Pay Calculator
Work out UK statutory redundancy pay from date of birth, employment dates and weekly pay, using the current age multipliers and pay cap.
Open tool →UK Holiday Entitlement Calculator
Work out UK statutory holiday entitlement for regular hours, or the 12.07% accrual for irregular hours and part-year workers.
Open tool →Pension Annual Allowance Calculator
Work out your UK pension annual allowance for 2026/27, including the tapered annual allowance, the Money Purchase Annual Allowance, and carry forward.
Open tool →Child Benefit & High Income Tax Charge Calculator
Work out your UK Child Benefit and the High Income Child Benefit Charge (HICBC) if the higher earner's income is over £60,000.
Open tool →UK Corporation Tax Calculator
Work out UK Corporation Tax, including marginal relief for profits between £50,000 and £250,000, adjusted for associated companies.
Open tool →UK Tax Year Dates & Self Assessment Deadlines
Find the start and end of any UK tax year, plus the Self Assessment filing and payment deadlines, including both payments on account.
Open tool →MOT Due Date Calculator
Work out when a car, motorcycle or light van needs its next MOT test, including the window for testing it early without losing the renewal date.
Open tool →UK Self Assessment Tax Calculator
Estimate your UK Self Assessment bill: Income Tax, Class 2/4 NI, student loan, your balancing payment and Payments on Account.
Open tool →Landed Cost Calculator
Add shipping, insurance, customs duty and import VAT to a product's cost to see its true landed cost per unit.
Open tool →Speed Converter
Convert speed between km/h, mph, m/s, knots and Mach instantly, free.
Open tool →Pressure Converter
Convert pressure between psi, bar, kPa, atm, mmHg, inHg and torr instantly, free.
Open tool →Correlation & Linear Regression Calculator
Work out the Pearson correlation coefficient and a best-fit line (slope, intercept, R²) from x,y data pairs.
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