Calculators
Everyday maths for money, study, health and time.
Tools last updated
Practical calculators for the numbers that come up in real life: loan repayments, exam grades, percentages, attendance and more. Each one shows the formula it used and explains the result, so you can check the working rather than trust a black box.
Most used
All 30 Calculators
30 tools
Percentage CalculatorWork out percentages, increases, decreases and 'what percent of'.Age CalculatorFind an exact age in years, months, days — and the next birthday.GPA CalculatorAdd your courses and credits to get a weighted grade point average.CGPA CalculatorCombine several semesters into one cumulative grade average.Grade CalculatorTurn marks into a percentage and a letter grade.Attendance CalculatorSee your attendance percentage and how many classes you still need.EMI CalculatorMonthly instalment, total interest and a full repayment schedule.Loan CalculatorCompare loan amounts, rates and terms with an amortisation table.Mortgage CalculatorHome price, deposit, taxes and insurance in one monthly figure.Compound Interest CalculatorProject savings growth with regular contributions.BMI CalculatorBody mass index in metric or imperial, with the healthy weight range.Discount CalculatorSale price, money saved, and stacked or reverse discounts.Tax CalculatorAdd or remove sales tax, VAT or GST from any amount.Salary CalculatorConvert between hourly, weekly, monthly and yearly pay.Scientific CalculatorTrigonometry, logs, powers and parentheses with a full history.Paint and Wallpaper CalculatorWork out how much paint or wallpaper a room needs, down to the tins to buy.Pet Age CalculatorConvert a dog's or cat's age to human years, adjusted for size and breed.Take-Home Pay CalculatorSee salary after tax for the UK, Canada, Australia or India, with every deduction.EV Charging Cost CalculatorWork out what charging an electric car costs, per charge, per mile or per km.Subscription Cost TrackerList your subscriptions to see the real monthly and yearly cost, then print it.Tip CalculatorWork out the tip and split the bill between any number of people.Date CalculatorCount the days or working days between two dates, or add days to a date.Time Card CalculatorAdd up a week's hours from start and finish times, with breaks, overtime and pay.Fuel Cost CalculatorWork out the fuel cost of a trip from distance, mpg or L/100 km and the fuel price.Unit Price CalculatorCompare pack sizes by price per 100 g, per kg, per litre or per item.SIP CalculatorProject what a monthly SIP grows to, with an optional yearly step-up.BMR and Calorie CalculatorEstimate your basal metabolic rate and daily calories with the Mifflin-St Jeor equation.Loan Comparison CalculatorCompare up to three loans by monthly payment, total interest, fees and true rate.Savings Goal CalculatorFind the monthly saving needed to reach a goal, or how long it will take.Time Duration CalculatorHours and minutes between two times, a time plus a duration, or a column of durations added up.
What these calculators cover
The calculators here explain how each result was reached — most show the formula and a worked example — so you can follow the arithmetic instead of taking a number on trust. They group into money, study and everyday sums.
Money
For borrowing, the EMI Calculator gives the monthly instalment and a month-by-month schedule, the Loan Calculator compares weekly, fortnightly and monthly repayments, and the Mortgage Calculator adds property tax and insurance to the monthly figure. The Compound Interest Calculator projects savings with regular contributions.
For pay, the Salary Calculator converts between hourly, weekly, monthly and yearly figures before tax, and the Take-Home Pay Calculator estimates pay after tax for the UK, Canada, Australia and India, listing every deduction. For prices, the Discount Calculator handles stacked and reverse discounts and the Tax Calculator adds or removes sales tax, VAT or GST. The Subscription Cost Tracker and EV Charging Cost Calculator turn scattered charges into a figure you can compare.
Study
The Percentage Calculator answers the four common percentage questions. The Grade Calculator turns marks into a percentage and a letter grade and works out what you need on a final exam. The GPA Calculator and CGPA Calculator weight grades by credits, and the Attendance Calculator tells you how many classes you can miss, or must attend, to stay above a requirement.
Health and everyday sums
The BMI Calculator gives body mass index with the healthy weight range for your height. The Age Calculator counts real calendar days, including leap years, and the Pet Age Calculator converts a dog's or cat's age to human years. The Paint and Wallpaper Calculator works out how much paint or wallpaper a room needs, and the Scientific Calculator handles trigonometry, logarithms and powers with a history of what you entered.
How to read the results
- Loan and mortgage figures are estimates, not quotes. Lenders add fees and insurance and use their own rounding, so confirm the numbers with the lender before committing. Nothing here is financial advice.
- Tax rules change every year. The take-home pay calculator states the tax year it uses for each country. It is a guide to what to expect, not a substitute for a payslip or a tax adviser.
- Grade boundaries and GPA scales belong to your institution. The percentage is the reliable figure; the letter depends on whose table you use.
- BMI is a screening measure, not a diagnosis. Speak to a healthcare professional about your own situation.
All of these run in your browser. The figures you type — salaries, loan amounts, weight — are not sent anywhere.
Guides
- How to turn a test score into a percentage and a letter gradeConvert any score such as 61/80 into a percentage and a letter grade, see common scores out of 80, and work out what you need on the final.
- How EMI is calculated — with a worked exampleThe EMI formula explained in plain words, a worked loan example, why early payments are mostly interest, and what a longer tenure really costs.
- How to calculate your GPA (and CGPA)Work out a credit-weighted GPA step by step, see why big courses count more, handle pass/fail courses, and combine semesters into a CGPA.
- What your BMI means — and what it cannot tell youHow BMI is calculated, what the WHO categories mean, the healthy weight range for your height, and the real limits of BMI for individuals.
- How to calculate percentage change — and the mistakes everyone makesThe percentage change formula with worked examples, why a rise and a fall of the same size are different percentages, and percent versus percentage points.
- How to add or remove VAT, GST or sales tax from a priceAdd tax to a net price, take it out of a gross price the right way, and see why subtracting the percentage gives the wrong answer — with worked examples.
- Compound interest explained, with real numbersHow compound interest works, how much compounding frequency really matters, the rule of 72, and why starting early beats almost everything else.
- How to convert hourly pay to an annual salary, and backTurn an hourly rate into a yearly, monthly or weekly figure and back again, avoid the four-weeks-a-month mistake, and compare job offers fairly.
- How much paint do I need? Measuring a room properlyMeasure a room, work out the wall area, allow for doors, windows and coats, and turn it into the right number of tins — with metric and imperial examples.
- How to calculate attendance percentage — and how many classes you can missWork out your attendance percentage, how many classes you can still miss above a 75% requirement, and how many you need to attend to get back above it.
- How to calculate an exact age in years, months and daysWhy dividing by 365 gives the wrong age, how to count years, months and days, what happens to 29 February birthdays, and how to find an age on a cut-off date.
- Dog years to human years: why the ×7 rule is wrongHow old a dog or cat really is in human terms, why size changes the answer, what a DNA study found, and a quick chart for small, medium, large and giant dogs.
- How much does it cost to charge an electric car?Work out the cost of a charge and the cost per mile or kilometre for an electric car, see why public rapid charging changes the picture, and compare with petrol.
- What goes into a mortgage payment — principal, interest, taxes and insuranceBreak a monthly mortgage payment into its parts, see how the deposit, rate and term change it, and why the total interest over 30 years is so large.
- UK take-home pay in 2026/27: how income tax and National Insurance are worked outHow UK income tax and National Insurance turn a salary into take-home pay in the 2026/27 tax year, with worked examples, the £100,000 trap and student loans.
- How to calculate a discount, a sale price and a stacked offerWork out a sale price, the real saving from stacked discounts, an original price from a sale price, and whether a multi-buy is actually a bargain.
- Weekly, fortnightly or monthly loan payments: which costs less?How payment frequency changes the total interest on a loan, why the saving is small unless you pay more, and how “accelerated” fortnightly payments work.
- Order of operations: why 2 + 3 × 4 is 14, not 20The rules a scientific calculator follows — brackets, powers, multiplication and division, addition and subtraction — plus degrees versus radians and common errors.
- Currency conversion: the real rate, the bank's rate and the hidden feesWhat the mid-market exchange rate is, why your bank or card gives less, how to compare providers, and the card-terminal choice that costs travellers money.
- Height in feet and inches to centimetres, and backConvert a height between feet and inches and centimetres exactly, with a quick reference table and the mistakes that put conversions an inch out.
- Acres, hectares, square feet and local land units explainedConvert land and floor areas between acres, hectares, square metres and square feet, picture how big each one is, and handle local units such as ropani and cent.
- Engine cc, litres and horsepower: what the numbers meanConvert engine size between cc, litres and cubic inches exactly, see why horsepower can only be estimated from engine size, and decode hp, bhp, PS and kW.
- How to make an invoice that gets paid on timeWhat to put on an invoice, how to number it, clear payment terms, tax and discounts, and how to create a professional PDF invoice without an account.
- Reverse percentages: how to find the original numberA price after a 20% rise is 96, so what was it before? How to work backwards from a percentage increase, discount or tax, and the common mistake that gives 76.8.
- Percentage points vs percent: what is the difference?An interest rate rising from 4% to 5% is up one percentage point but 25 percent. Why the two are different, when to use each, and how headlines mislead with them.
- Markup vs margin: how to price for the profit you wantAdding 40% to cost does not give a 40% margin. The difference between markup and margin, a conversion table, and the formula to price for a target margin.
- How to calculate your salary increase percentageWork out your pay rise as a percentage, find the new salary from a percentage raise, compare it with inflation, and see what it means per month and per hour.
- Flat rate vs reducing balance interest: why 10% flat costs moreA 10% flat rate loan costs far more than a 10% reducing balance loan. A worked example, the equivalent reducing rate, and how to compare loan offers fairly.
- Loan prepayment: should you reduce the EMI or the tenure?After a part-prepayment, lenders ask whether to cut your monthly payment or the number of months left. A worked example shows which saves more interest, and when.
- How much car loan can I afford?Start from a monthly payment you can live with and work backwards to the loan amount. Worked figures for 3 to 6 years, the total cost, and the costs beyond the loan.
- How much deposit do you need to buy a house?5%, 10% or 20%? How the size of your deposit changes the monthly payment, the interest over the term and the rate you are offered, with a worked example.
- APR vs interest rate: which number to compareThe interest rate is what you pay on the balance; APR adds the fees. A worked example where an 8% loan has an APR of 10%, and how to compare loans fairly.
- The rule of 72: how long it takes money to doubleDivide 72 by the interest rate to estimate how many years money takes to double. How accurate the shortcut is, and how it works for inflation and debt.
- How much will a monthly investment grow to? (SIP returns explained)What 5,000 a month becomes after 5, 10, 15 and 20 years at 12%, why the later years add most of the growth, and what these projections can and cannot promise.
- How fixed deposit interest is calculated with quarterly compoundingWhy a 7% fixed deposit pays more than 7% a year, a worked example for 1,00,000 over five years, and how payout options and tax change what you receive.
- How to calculate overtime pay (time and a half, double time)Work out time-and-a-half and double-time pay from an hourly rate or a salary, with a worked weekly example, and check your payslip for the usual mistakes.
- Pro rata salary: how part-time and part-year pay is worked outA job advertised at 30,000 pro rata for 22.5 hours a week pays 18,000. How to calculate pro rata pay, holiday and part-year salaries, with worked examples.
- CTC vs in-hand salary: why 12 LPA is not 1 lakh a monthAn Indian job offer quotes cost to company, not what reaches your bank. What CTC includes, a worked example for 12 lakh, and how to estimate monthly in-hand pay.
- How to convert CGPA to percentageCBSE multiplies CGPA by 9.5, but universities use their own formulas. How each one works, a worked example, and what to write when a form asks for a percentage.
- What grade do I need on my final exam?Work out the final exam score you need for the overall grade you want, from your current grade and the exam's weight, with worked examples and the formula.
- Weighted vs unweighted GPA: what is the difference?Why one transcript can show a 3.5 and a 3.9 for the same student. How weighted GPA rewards honors and AP classes, a worked example, and what colleges look at.
- How to calculate age on a specific date (for exam and job eligibility)Exam and job notices set age limits as on a cut-off date. How to work out your exact age on that date, read born-between ranges, and avoid the leap-day traps.
- How to count the days between two datesCount days, weeks and months between two dates, decide whether to include the end date, and avoid the month-length and leap-year mistakes of counting by hand.
- Cat years to human years: how old is my cat?A one-year-old cat is roughly 15 in human years and a two-year-old about 24. The chart vets use, cat life stages, and what changes as your cat gets older.
- What is a healthy weight for my height?The healthy weight range for your height in kilograms and pounds, how it is worked out from BMI, and why it is a range rather than a single ideal number.
- BMI cut-offs for Asian adults: why 23 mattersFor people of South Asian, Chinese and other Asian backgrounds, health risks rise at a lower BMI. The 23 and 27.5 cut-offs, their origin and how to use them.
- How many rolls of wallpaper do I need?Count wallpaper the way decorators do: by drops, not by area. A worked example, how pattern repeat changes the answer, and why to buy from one batch.
- Why sin(30) gives −0.988: degrees vs radians on a calculatorIf sin(30) does not give 0.5, your calculator is in radian mode. How to tell, how to switch, how to convert between degrees and radians, and when to use each.
- How to convert minutes to decimal hours for timesheets7 hours 45 minutes is 7.75 hours, not 7.45. A minutes-to-decimal table, the formula, and how to avoid the most common timesheet and invoicing mistake.
- Invoice vs receipt vs quote vs estimate: which document whenA quote offers a price, an invoice asks for payment and a receipt proves it was paid. What each document is for, what goes on it, and where pro forma invoices fit.
- Why you can’t just average percentagesAveraging 90% and 60% gives 75%, but your real score may be 63%. Why percentages with different bases need a weighted average, and how to do it right.
- Why percentages don’t add up to 100% — and how to fix itA breakdown shows 33%, 33% and 33%, or 101% in total. Rounding, overlapping answers and different bases are why. How to present figures that add up honestly.
- Will a pay rise put me in a higher tax bracket and cut my take-home pay?A higher tax band only taxes the extra at the higher rate, so take-home pay still rises. How bands work, a UK example, and the real catches to watch for.
- Why your EMI calculation doesn’t match the bank’s figureAn online EMI result a few rupees or dollars off the lender's quote is normal. Fees, rounding, first-month interest and rate type explain most differences.
- Why 1.5% a month is not 18% a yearA monthly rate × 12 understates the yearly cost when interest compounds: 1.5% a month is about 19.6% a year. How to convert monthly and annual rates.
- Tip before or after tax? And does the discount come first?Should you tip on the pre-tax or post-tax total, or the price before a coupon? What's customary, how big the difference is, and when the order matters.
- Why an invoice’s tax total is off by a centTax rounded on each line rarely matches tax on the total. Why one-cent gaps appear between invoices, spreadsheets and accounts, and how to pick one rule.
- Buy one get one free, 3 for 2, second half price: what discount is it really?Buy one get one free is 50% off only if you want two. The real percentage behind 3 for 2, second item half price and buy 2 get 1 half price, and how to compare.
- Celsius to Fahrenheit in your head: the shortcut and where it fails“Double it and add 30” is close for weather but wrong for fevers and ovens. How accurate it is, a better mental method, and reference points to remember.
- Square metres vs metres squared: area conversion mistakesWhy 1 m² is 10.76 square feet, not 3.28, why “2 metres squared” is ambiguous, and how to convert areas and volumes without the most common mistakes.
- Stones and pounds to kg: why 11.5 stone isn’t 11 st 5 lbA stone is 14 pounds, so decimal stones and stones-and-pounds are not the same. How to convert st and lb to kg and back, with worked examples and a quick check.
- Ton vs tonne: metric, short and long tons explainedA tonne is 1,000 kg, a US short ton 907 kg, and a UK long ton 1,016 kg. Which one a document means, why air conditioners are rated in tons, and how to convert.
- Troy ounce vs ounce: why gold is weighed differentlyGold and silver prices are per troy ounce, 31.1 g, not the 28.35 g ounce on kitchen scales. How to convert troy ounces to grams and check what a price means.
- kW vs kWh: the difference, and why your bill uses kWhkW is how fast energy is used; kWh is how much is used. How to turn appliance power into energy and cost, and how EV battery and charger figures fit together.
- Monthly vs annual subscription: when the yearly plan really savesAn annual plan is cheaper only if you keep it long enough. How to find the break-even month, compare weekly, monthly and yearly prices, and spot renewal traps.