Calculators
Eight calculators for everyday numbers: a loan payment, a discount, a split bill, an exact age, a unit conversion. Each one updates as you type and is upfront about what it leaves out.
None of them sends what you enter anywhere. That is worth saying for a calculator, because the inputs are so often personal ā your weight, the size of your mortgage, your date of birth.
All tools 8
Age Calculator
Exact age & date difference.
āBMI Calculator
Body Mass Index & category.
āLoan / Mortgage Calculator
Monthly payment & total interest.
āPercentage Calculator
Percent of, is-what-%, % change.
āDiscount & Tax Calculator
Final price after discount & tax.
āBill Splitter & Tip
Split the check & calculate the tip per person.
āBuy & Trade Calculator
Resale cash & store-credit offers from your buy/trade %.
āUnit Converter
Length, weight, temperature & volume.
āWhich calculator for which question
- What will the monthly payment be?The Loan / Mortgage Calculator takes the price, your deposit, the interest rate and the term, and returns the monthly payment, the total interest and what the purchase really costs you overall.
- What is 18% of 64? What percentage is 43 out of 60?The Percentage Calculator answers the three everyday questions on one card: a percentage of a number, one number as a percentage of another, and the percentage change between two values.
- What will I pay after the discount and sales tax?The Discount & Tax Calculator shows how much you save, the reduced price, and the final price with tax added.
- How do we split this bill?The Bill Splitter & Tip adds a tip of 0 to 40% and divides the total between any number of people, with an option to round each share up to a whole amount.
- Exactly how old is someone, or how many days until a date?The Age Calculator gives the gap between two dates in years, months and days, and again as total months, weeks and days.
- What is my BMI?The BMI Calculator works in metric or imperial units and shows which of the four standard categories the result falls in.
- How many kilometres is five miles?The Unit Converter covers length, weight, temperature and volume.
- What should I offer for this trade-in?The Buy & Trade Calculator is a counter tool for resale shops: list items with their resale value and it quotes a cash offer and a store-credit offer from your own percentages.
Limits worth knowing
- The loan figure is principal and interest only. A real mortgage payment usually adds property tax and insurance, so budget above the number shown. The calculator assumes a fixed rate compounded monthly and has no amortization schedule.
- Use the interest rate, not the APR. APR includes fees, so entering it overstates the payment.
- Two discounts do not add up. Twenty percent off and then another ten is 28% off, not 30%, because the second applies to the already reduced price.
- Percentage change depends on where you start. From 80 to 100 is +25%; from 100 back to 80 is ā20%.
- BMI is a screening number, not a diagnosis. It compares weight with height and cannot tell muscle from fat. The categories shown are the standard adult ones and do not apply to children or teenagers.
- Volume units are US customary. A UK pint and gallon are about 20% larger than the US ones. A tonne here is the metric tonne of 1,000 kg.
- Amounts are shown with a dollar sign, but the arithmetic is the same in any currency.
- The bill splitter divides evenly. It does not itemise who ordered what.
How these tools work
Each calculator is a short piece of JavaScript running standard formulas as you type. The loan calculator uses the usual amortization formula, monthly payment = PĀ·i Ć· (1 ā (1 + i)ān), where P is the amount borrowed, i the monthly rate and n the number of payments. BMI is weight divided by height squared. Age is calendar arithmetic that accounts for leap years and the different lengths of months. Nothing is stored, with one exception: the buy & trade calculator keeps your item list and percentages in this browser, so a closed tab picks up where you left off.
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Frequently asked questions
Does the loan calculator include taxes and insurance?
No. It shows principal and interest only. Property tax, home insurance, mortgage insurance and any fees are extra, so treat the monthly figure as the minimum rather than the full cost of owning the property.
Is what I type into these calculators saved?
No. The figures exist only in the page and disappear when you reload or close the tab. The one exception is the buy and trade calculator, which deliberately saves your list and percentages in your own browser so you can use it through a working day.
Why do two percentage discounts not add up?
Because the second discount is taken from the reduced price, not the original one. With 20 percent off, a 100 item costs 80; a further 10 percent off takes 8 from that, leaving 72. The combined discount is 28 percent.
Is BMI a reliable measure of health?
It is a quick screening measure, not a diagnosis. It uses only height and weight, so it cannot distinguish muscle from fat and says nothing about where weight is carried. It is a reasonable starting point for a conversation with a doctor, not a substitute for one.
How accurate are the results?
The calculators use the standard formulas and round money to cents. They are accurate for the assumptions stated on each page. For a decision with real money at stake, such as a mortgage, confirm the figures with your lender, who will include fees and terms these tools do not know about.