Calculator Guides
Each guide explains what a calculator does, the formula behind it, a worked example, tips and the mistakes people make. Pick a guide below, or search.
Financial guides (73)
- 401(k) CalculatorThe 401(k) calculator estimates your retirement balance including your contributions, an employer match and yearly salary growth.
- Amortization CalculatorAn amortization schedule shows how each year of loan payments is split between interest and principal and what balance remains.
- Annuity CalculatorThe annuity calculator values a stream of equal payments: what it is worth today and what it will grow to.
- Annuity Payout CalculatorThis tool shows the monthly income a lump sum could pay over a chosen number of years.
- APR CalculatorThe APR calculator shows the true yearly cost of a loan including upfront fees.
- Auto Lease CalculatorThe auto lease calculator estimates the monthly payment of a car lease.
- Auto Loan CalculatorThe auto loan calculator works out the monthly payment for a car loan after your down payment, trade-in and sales tax.
- Average Return CalculatorThe average return calculator shows the annualised growth rate (CAGR) between a start and end value.
- Boat Loan CalculatorThe boat loan calculator estimates monthly payments for a boat after your down payment.
- Bond CalculatorThe bond calculator prices a bond from its coupon, market yield and years to maturity.
- Business Loan CalculatorThe business loan calculator shows payment, fees and the effective APR including an origination fee.
- Canadian Mortgage CalculatorThe Canadian mortgage calculator uses semi-annual compounding, as required for fixed-rate mortgages in Canada.
- Cash Back or Low Interest CalculatorThis tool compares a cash-back offer with a low-interest loan so you can see which costs less.
- CD CalculatorThe CD calculator shows the value of a certificate of deposit at maturity and the effective yield.
- College Cost CalculatorThis tool projects the future cost of a degree and the monthly saving needed to cover the gap.
- Commission CalculatorThe commission calculator shows commission earned on a sale and your share if it is split.
- Compound Interest CalculatorThe compound interest calculator shows growth when interest is added back to the balance and also earns interest.
- Credit Card CalculatorThe credit card calculator shows how long a fixed monthly payment takes to clear a balance and what the interest costs.
- Credit Cards Payoff CalculatorThis tool works out the payment needed to clear card debt by a chosen date.
- Currency CalculatorThe currency calculator converts an amount using an exchange rate that you enter, and can include a fee.
- Debt Consolidation CalculatorThis tool compares your current debts with a single consolidation loan so you can see the payment and interest difference.
- Debt Payoff CalculatorThe debt payoff calculator shows how paying extra each month shortens your payoff time and saves interest.
- Debt-to-Income Ratio CalculatorThe DTI calculator shows what share of your monthly gross income goes to debt payments, which lenders use to judge loans.
- Depreciation CalculatorThis tool shows how an asset loses value year by year using straight-line or double-declining balance methods.
- Discount CalculatorThe discount calculator gives the sale price after a percentage off, with an optional extra discount.
- Down Payment CalculatorThe down payment calculator shows how much to put down and how much to save each month to reach it.
- Estate Tax CalculatorThe estate tax calculator estimates US federal estate tax on the value above the exemption.
- FHA Loan CalculatorThe FHA loan calculator estimates payments including the upfront and annual mortgage insurance premiums.
- Finance CalculatorThe finance calculator solves a time-value-of-money problem: future value, present value, payment, time or interest rate.
- Future Value CalculatorThe future value calculator shows what a starting amount plus regular deposits will be worth later.
- HELOC CalculatorThe HELOC calculator shows your available credit line and the interest-only payment on what you draw.
- Home Equity Loan CalculatorThis tool estimates how much you could borrow against your home and the payment.
- House Affordability CalculatorThis tool estimates the home price you can afford from your income, debts, deposit and interest rate using the common 28/36 rule.
- Income Tax CalculatorThis tool estimates income tax and payroll tax for the UK (2025/26) or the US federal system (2025), plus your take-home pay.
- Inflation CalculatorThe inflation calculator shows how a steady yearly price rise changes what your money buys over time.
- Interest CalculatorThis simple-interest tool shows how much interest a fixed rate earns or costs when interest is not compounded.
- Interest Rate CalculatorThis calculator finds the interest rate hidden in a loan quote, given the amount, the monthly payment and the term.
- Investment CalculatorThe investment calculator shows how a starting sum plus regular monthly additions could grow at an assumed return.
- IRA CalculatorThe IRA calculator projects a traditional IRA balance and shows an approximate after-tax value using your expected retirement tax rate.
- IRR CalculatorThe IRR calculator finds the annual return that makes the present value of a series of cash flows equal zero.
- Lease CalculatorThe lease calculator estimates a payment when you rent an asset and return it at the end.
- Loan CalculatorThe loan calculator shows the monthly payment, total interest and yearly balance of a fixed-rate loan.
- Margin CalculatorThe margin calculator shows profit margin and markup from your cost and selling price.
- Mortgage Amortization CalculatorThis tool shows how a mortgage balance falls year by year and how much of each year's payments goes to interest and principal.
- Mortgage CalculatorA mortgage calculator shows the monthly cost of a home loan and how much interest you will pay over its life.
- Mortgage Calculator UKThe UK mortgage calculator shows repayment and interest-only monthly payments for a home in pounds.
- Mortgage Payoff CalculatorThe mortgage payoff calculator shows how much sooner you finish your loan, and how much interest you save, by paying extra each month.
- Mutual Fund CalculatorThis tool shows how a fund's expense ratio reduces your final balance over time.
- Payback Period CalculatorThe payback period calculator shows how long an investment takes to earn back its cost.
- Payment CalculatorThe payment calculator solves two common questions: what monthly payment repays a balance in a set time, and how long a chosen payment will take.
- Pension CalculatorThe pension calculator estimates annual pension from a defined-benefit scheme.
- Percent Off CalculatorThis calculator shows the price after a percent off and how much you save.
- Personal Loan CalculatorThe personal loan calculator shows monthly payments, total cost and the yearly interest breakdown for an unsecured loan.
- Present Value CalculatorThe present value calculator tells you what a future amount is worth today at a given discount rate.
- Real Estate CalculatorThis tool shows the full monthly cost of owning a home including taxes, insurance, HOA and maintenance.
- Refinance CalculatorThe refinance calculator compares your current loan with a new one and shows the monthly saving and break-even time.
- Rent CalculatorThe rent calculator estimates how much rent you can afford from your income and debts.
- Rent vs. Buy CalculatorThe rent vs buy calculator compares the net cost of buying with renting over a chosen number of years.
- Rental Property CalculatorThe rental property calculator estimates cash flow, cap rate and cash-on-cash return for an investment home.
- Repayment CalculatorThe repayment calculator shows how long a fixed monthly payment takes to repay a loan and the total interest.
- Retirement CalculatorThe retirement calculator projects how large your savings could be at retirement and roughly what monthly income they could support.
- RMD CalculatorThe RMD calculator estimates the minimum you must withdraw from a retirement account each year using the IRS Uniform Lifetime Table.
- ROI CalculatorThe ROI calculator shows total and annualised return on an investment.
- Roth IRA CalculatorThe Roth IRA calculator projects growth of contributions that can be withdrawn tax-free in retirement, if rules are met.
- Salary CalculatorThe salary calculator converts pay between hourly, daily, weekly, two-weekly, monthly and yearly amounts using your hours and weeks.
- Sales Tax CalculatorThe sales tax calculator adds tax to a price, or removes it from a total to find the pre-tax price.
- Savings CalculatorThe savings calculator shows how a starting balance and regular deposits grow at a given interest rate.
- Simple Interest CalculatorThe simple interest calculator adds up interest on a loan or deposit that does not compound, with an option to include extra months.
- Student Loan CalculatorThe student loan calculator shows the standard monthly payment, the total interest and the effect of paying extra.
- Take-Home-Paycheck CalculatorThe take-home calculator estimates net pay per paycheck from gross pay using a flat effective tax rate.
- Tip & Bill SplitterThe tip and bill splitter works out the tip, the total and what each person owes.
- VA Mortgage CalculatorThe VA mortgage calculator estimates payments for a VA-backed loan including the funding fee.
- VAT CalculatorThe VAT calculator adds value-added tax to a net price or removes it from a gross price.
Health & Fitness guides (28)
- Army Body Fat CalculatorThis calculator uses the circumference method that the U.S.
- BAC CalculatorThe BAC calculator gives a rough estimate of blood alcohol concentration using the Widmark formula.
- BMI CalculatorThe BMI calculator shows your Body Mass Index, a quick screening number based on height and weight for adults.
- BMR CalculatorBasal metabolic rate is the energy your body burns at complete rest.
- Body Fat CalculatorThis tool estimates body fat percentage from tape measurements using the U.S.
- Body Surface Area CalculatorBody surface area is used in medicine to dose some treatments.
- Calorie CalculatorThe calorie calculator estimates how many calories you need to maintain, lose or gain weight.
- Calories Burned CalculatorThis tool estimates calories burned in an activity from its MET value, your weight and the time.
- Carbohydrate CalculatorThis tool turns a calorie target and carb share into grams of carbohydrate.
- Conception CalculatorThe conception calculator estimates your likely ovulation and fertile window from your cycle.
- Due Date CalculatorThe due date calculator estimates a due date from your last period, conception date or an IVF transfer.
- Fat Intake CalculatorThis tool shows how many grams of fat fit within your calories.
- GFR CalculatorThe GFR calculator estimates kidney filtration (eGFR) from age, sex and blood creatinine using the CKD-EPI 2021 equation.
- Healthy Weight CalculatorThis tool gives the weight range that corresponds to a healthy BMI of 18.5 to 24.9 for your height.
- Ideal Weight CalculatorThe ideal weight calculator shows what four classic formulas suggest for a given height and sex.
- Lean Body Mass CalculatorLean body mass is everything except fat.
- Macro CalculatorThe macro calculator splits your daily calories into grams of protein, carbohydrate and fat for a chosen plan.
- One Rep Max CalculatorThe one rep max calculator estimates the most you could lift once from a lighter set.
- Overweight CalculatorThe overweight calculator shows your BMI category and how much weight to lose to reach a BMI of 24.9.
- Ovulation CalculatorThe ovulation calculator predicts your fertile window and next period.
- Pace CalculatorThe pace calculator converts distance and time into pace and speed and projects race times.
- Period CalculatorThe period calculator predicts the dates of your next three periods.
- Pregnancy CalculatorThe pregnancy calculator estimates your due date and current week from the first day of your last period.
- Pregnancy Conception CalculatorThis tool estimates when conception likely happened from your due date.
- Pregnancy Weight Gain CalculatorThis tool shows the recommended weight gain in pregnancy based on pre-pregnancy BMI, using the Institute of Medicine ranges.
- Protein CalculatorThe protein calculator estimates daily protein from your body weight and goal.
- Target Heart Rate CalculatorThe target heart rate calculator shows training zones from your age and resting heart rate.
- TDEE CalculatorTotal daily energy expenditure is the calories you burn in a day including activity.
Math guides (45)
- Area CalculatorThe area calculator finds the area of common 2D shapes.
- Average CalculatorThe average calculator finds the mean of a list of numbers, along with their sum and count.
- Basic CalculatorThe basic calculator handles everyday sums with memory keys and a running tape of your recent answers.
- Big Number CalculatorThe big number calculator does exact arithmetic on very large whole numbers.
- Binary CalculatorThe binary calculator adds, subtracts, multiplies and divides binary numbers and shows decimal, hex and octal.
- Circle ToolsCircle Tools find the radius, diameter, circumference and area of a circle from any one of them.
- Common Factor CalculatorThe common factor calculator lists the factors shared by two or more numbers.
- Confidence Interval CalculatorThe confidence interval calculator gives a range likely to contain the true mean.
- Distance CalculatorThis tool finds the straight-line distance between two points in 2D or 3D.
- Exponent CalculatorThe exponent calculator raises a number to a power.
- Factor CalculatorThe factor calculator lists all factors of a whole number and tells you if it is prime.
- Fraction CalculatorThe fraction calculator adds, subtracts, multiplies or divides two fractions and simplifies the answer.
- Greatest Common Factor CalculatorThe GCF calculator finds the largest number that divides all numbers in a list.
- Half-Life CalculatorThe half-life calculator shows how much of a decaying substance remains after a given time.
- Hex CalculatorThe hex calculator works with hexadecimal numbers, which use 0–9 and A–F.
- Least Common Multiple CalculatorThe LCM calculator finds the smallest number that is a multiple of every number in a list.
- Log CalculatorThe log calculator finds the logarithm of a number to any base.
- Long Division CalculatorThe long division calculator shows quotient, remainder and decimal result.
- Maths CalculatorThe Maths Calculator evaluates a full sum you type, with brackets, powers, roots, trigonometry and logarithms.
- Matrix CalculatorThe matrix calculator works with 2×2 matrices: add, subtract, multiply, determinant and inverse.
- Mean Median Mode Range CalculatorThis calculator finds the mean, median, mode and range of a data set.
- Number Sequence CalculatorThis tool works with arithmetic and geometric sequences, giving the nth term and the sum.
- P-value CalculatorThe p-value calculator converts a z-score to a p-value for a one- or two-tailed test.
- Percent Error CalculatorThe percent error calculator compares a measured value with a true value.
- Percentage CalculatorThe percentage calculator answers the four most common percent questions: percent of a number, percent change, adding a percent and removing a percent.
- Permutation and Combination CalculatorThis tool counts ordered arrangements (permutations) and unordered selections (combinations).
- Prime Factorization CalculatorThe prime factorization calculator writes a number as a product of primes.
- Probability CalculatorThis tool shows probabilities of two independent events happening together or separately.
- Pythagorean Theorem CalculatorThe Pythagorean theorem calculator finds a missing side of a right triangle.
- Quadratic Formula CalculatorThe quadratic calculator solves ax² + bx + c = 0 and shows the vertex.
- Random Number GeneratorThe random number generator picks numbers in a range, with or without duplicates.
- Ratio CalculatorThe ratio calculator solves proportions such as A : B = C : D.
- Right Triangle CalculatorThe right triangle calculator gives the missing side, area, perimeter and angles.
- Root CalculatorThe root calculator finds the nth root of a number.
- Rounding CalculatorThe rounding calculator rounds a number to a chosen number of decimal places using different methods.
- Sample Size CalculatorThe sample size calculator shows how many people you need to survey for a chosen confidence level and margin of error.
- Scientific CalculatorThe scientific calculator adds trigonometry, logarithms, powers, roots and factorials to the basic keys.
- Scientific Notation CalculatorThis tool converts a number to scientific and engineering notation.
- Slope CalculatorThe slope calculator finds the slope, angle, distance and line equation through two points.
- Standard Deviation CalculatorThe standard deviation calculator shows how spread out a set of numbers is.
- Statistics CalculatorThe statistics calculator gives mean, median, mode, range, quartiles and standard deviation for a list of numbers.
- Surface Area CalculatorThe surface area calculator finds the outer area of common 3D shapes.
- Triangle CalculatorThe triangle calculator finds area, perimeter and angles from three side lengths.
- Volume CalculatorThe volume calculator finds the volume and surface area of a cube, box, cylinder, sphere or cone.
- Z-score CalculatorThe z-score calculator shows how many standard deviations a value is from the mean and its percentile.
Other guides (60)
- Age CalculatorThe age calculator gives your exact age in years, months and days between a birth date and another date.
- Bandwidth CalculatorThe bandwidth calculator estimates download time from file size and connection speed.
- Base64 Encode/DecodeThe Base64 tool encodes text to Base64 and decodes it back.
- Bra Size CalculatorThe bra size calculator estimates band and cup size from your underbust and bust measurements.
- BTU CalculatorThe BTU calculator estimates the cooling capacity a room needs.
- Concrete CalculatorThe concrete calculator estimates the volume of concrete and the number of bags for a slab.
- Darts Checkout CalculatorThe darts checkout calculator lists the best ways to finish a leg on a double with three darts or fewer from any score between 2 and 170.
- Date CalculatorThe date calculator adds or subtracts years, months and days from a date, or finds the number of days between two dates.
- Day CounterThe day counter shows days, weeks, weekdays and weekend days between two dates.
- Day of the Week CalculatorThe day of the week calculator tells you which weekday any date falls on.
- Density CalculatorThe density calculator finds density, mass or volume when you know the other two.
- Dew Point CalculatorThe dew point calculator finds the temperature at which air becomes saturated, from temperature and humidity.
- Dice RollerThe dice roller rolls any number of dice with 4 to 100 sides.
- Distance ConverterThe distance converter changes miles, kilometres, metres, feet and more.
- Electricity CalculatorThe electricity calculator estimates what an appliance costs to run.
- Engine Horsepower CalculatorThe engine horsepower calculator converts torque and engine speed to horsepower.
- Fuel Cost CalculatorThe fuel cost calculator estimates the fuel cost of a trip from distance, fuel economy and fuel price.
- Gas Mileage CalculatorThe gas mileage calculator finds fuel economy from miles driven and fuel used.
- GDP CalculatorThe GDP calculator adds up an economy's output using the expenditure approach.
- Golf Handicap CalculatorThe golf handicap calculator estimates your handicap index from your scores using the World Handicap System method.
- GPA CalculatorThe GPA calculator works out your grade point average from letter grades and credit hours.
- Grade CalculatorThe grade calculator shows what you need on the final exam to reach a target grade.
- Gravel CalculatorThe gravel calculator estimates the volume and weight of gravel for a driveway or path.
- Heat Index CalculatorThe heat index calculator shows how hot it feels when humidity is combined with temperature.
- Height CalculatorThe height calculator predicts a child's adult height from the parents' heights.
- Horsepower CalculatorThe horsepower calculator estimates a car's power from its weight and quarter-mile time.
- Hours CalculatorThe hours calculator finds hours worked between a start and end time minus a break, plus pay.
- IP Subnet CalculatorThe IP subnet calculator shows the network address, mask, broadcast address and host range for an IPv4 address and prefix.
- Mass CalculatorThe mass calculator finds mass from density and volume.
- Mileage CalculatorThe mileage calculator works out reimbursement for miles driven at a rate per mile.
- Molarity CalculatorThe molarity calculator finds a solution's concentration in moles per litre.
- Molecular Weight CalculatorThe molecular weight calculator adds up atomic masses for a chemical formula.
- Mulch CalculatorThe mulch calculator estimates the volume of mulch for a garden bed.
- Ohms Law CalculatorThe Ohm's law calculator finds voltage, current, resistance or power when you know any two.
- Online AbacusThe online abacus lets you slide beads to count from 1 to 50 and shows how an abacus represents numbers.
- Online StopwatchThe online stopwatch records time with laps and also works as a countdown timer.
- Password GeneratorThe password generator creates a random password in your browser using your length and character choices.
- Patio CalculatorThe patio calculator works out how many slabs and how much sub-base you need, with an allowance for cuts and breakages.
- Random Name PickerThe random name picker spins a wheel to choose a name at random.
- Resistor CalculatorThe resistor calculator reads a 4-band resistor colour code and shows the resistance and tolerance.
- Ring Size ConverterThe ring size converter changes ring sizes between US, UK, EU and Japanese systems.
- Roman Numeral ConverterThe Roman numeral converter changes numbers to Roman numerals and back.
- Roofing CalculatorThe roofing calculator estimates roof area, squares and shingle bundles.
- Shoe Size ConversionThe shoe size calculator converts US sizes to approximate UK and EU sizes.
- Sleep CalculatorThe sleep calculator suggests bedtimes or wake-up times that line up with the end of a 90-minute sleep cycle, so you are more likely to wake up feeling refreshed.
- Speed CalculatorThe speed calculator finds speed, distance or time from the other two.
- Square Footage CalculatorThis tool calculates the area of a room or lot and converts it between units.
- Stair CalculatorThe stair calculator finds the number of steps, riser height, run and stringer length for a staircase.
- Temperature ConverterThe temperature converter changes between Celsius, Fahrenheit and Kelvin.
- Tile CalculatorThe tile calculator finds how many tiles you need to cover an area.
- Time CalculatorThe time calculator adds or subtracts two times in hours, minutes and seconds.
- Time Card CalculatorThe time card calculator totals a week of in and out times and works out pay including overtime.
- Time Duration CalculatorThis tool finds the time between a start and end date and time.
- Time Zone CalculatorThe time zone calculator converts a date and time between two zones, including daylight saving.
- Tire Size CalculatorThe tire size calculator finds a tyre's diameter, sidewall height and revolutions per mile.
- Unit ConverterThe unit converter changes values between units of length, weight, temperature, volume, area, speed, time and data and shows the value in every unit at once.
- URL Encode/DecodeThe URL encoder converts special characters into percent-encoded form and decodes them back.
- Voltage Drop CalculatorThe voltage drop calculator estimates the voltage lost along a copper wire.
- Weight CalculatorThe weight calculator shows the force of gravity on a mass on different worlds.
- Wind Chill CalculatorThe wind chill calculator shows the feels-like temperature in cold, windy weather.