Eleven calculators on one page
Pick a tab and type. Every result updates as you go, and the line under it shows the formula with your numbers filled in, so you can check the working or copy it into your own notes. Each calculator remembers what you entered, in this browser only, so it is still there next time.
Percentages
- X% of Y is
X ÷ 100 × Y. 15% of 80 is 12. - X is what percent of Y is
X ÷ Y × 100. 30 is 25% of 120. - Percentage change from A to B is
(B − A) ÷ |A| × 100. Going from 80 to 100 is a 25% increase, while going back from 100 to 80 is a 20% decrease. - Increase or decrease by a percentage multiplies by
1 + X ÷ 100or1 − X ÷ 100. - Reverse percentage finds the number you started with. If a price is 230 after 15% was added, the original was
230 ÷ 1.15 = 200, not 230 minus 15%.
Age and dates
Age is counted the way people say it: whole years, then whole months, then the days left over. A month is counted from a date to the same date in the next month, and when that date does not exist, such as 31 April, the last day of the month is used. Leap years are handled by the calendar itself, so ages across 29 February come out right.
Days between two dates counts from the start date up to the end date, leaving the end date out unless you tick the box. Business days are Monday to Friday. Public holidays differ by country and region, so they are not removed; subtract any that fall in your range yourself.
Unit conversions
Conversions use the exact definitions: an inch is 25.4 mm, a pound is 0.45359237 kg, a US gallon is 3.785411784 litres and an imperial gallon is 4.54609 litres. Temperatures use their offset formulas, such as °F = °C × 9/5 + 32, rather than a single factor. Results are shown to 12 significant figures.
Data sizes come in two systems. Decimal units go up in steps of 1,000, so 1 GB is 1,000,000,000 bytes; drive makers and network speeds use these. Binary units go up in steps of 1,024, so 1 GiB is 1,073,741,824 bytes; memory, and the file sizes Windows shows as GB, use these. That is why a 1 TB drive appears as about 931 GB on a computer.
Mortgages and loans
The monthly payment comes from the standard formula for a fixed-rate loan, M = P × r ÷ (1 − (1 + r)^−n), where P is the amount borrowed, r is the yearly rate divided by 12 and n is the number of monthly payments. A loan of 300,000 at 5% over 25 years costs 1,753.77 a month.
The schedule then follows the loan month by month in whole cents, the way a lender does: each month's interest is the balance times r, rounded to the cent, and the rest of the payment reduces the balance. The last payment is adjusted so the balance lands exactly on zero. An extra monthly payment goes straight to the balance, which shortens the loan and cuts the interest; the result shows by how much. This is an estimate, not financial advice: property tax, insurance, fees and changes to a variable rate are not included.
Compound interest and savings goals
Savings grow by A = P(1 + r/n)^(nt), plus the growth of each regular deposit, where n is how often interest is added each year and t is the number of years. When deposits and compounding happen at different intervals, such as monthly deposits with daily compounding, each deposit earns the matching effective rate. The savings goal works the same formula backwards to find the deposit you need, rounded up to the cent so the goal is reached.
Tips, discounts and sales tax
Money is worked out in whole cents, and only rounded where a real bill would be. When a total does not split evenly, the split shows who pays the extra cent, so the shares add up to the total exactly. Stacked discounts are applied one after the other: 25% off and then another 10% off is 32.5% off in total, not 35%. Sales tax rates differ from place to place, so enter your own.
BMI
Body mass index is weight in kilograms divided by height in metres squared. The categories are the World Health Organization's adult ranges: under 18.5 underweight, 18.5 to 24.9 normal weight, 25 to 29.9 overweight, and 30 or more obesity, split into classes I, II and III. BMI is a quick screening number for groups of people. It cannot tell muscle from fat or say where weight is carried, so it is not a diagnosis, and it does not apply to children or during pregnancy.
GPA
Each grade is worth points on the 4.0 scale: A and A+ are 4.0, A− 3.7, B+ 3.3, B 3.0 and so on down to F at 0. GPA is the total of points times credits, divided by the total credits. Weighted GPA adds 0.5 for Honors courses and 1.0 for AP, IB or college courses, which is the most common method; some schools use other bonuses or count A+ as 4.3, so check your school's rules if the number matters.
Time
Add up hours and minutes for a timesheet, or take time away, and get the total in hours and minutes, in decimal hours for payroll and in minutes. Time between two times treats an end time earlier than the start as the next day, so a night shift from 22:30 to 06:15 comes out as 7 hours 45 minutes.
Privacy
There is no account, no analytics and no server behind this page. Every calculation runs in this browser, and nothing you enter is sent anywhere. Your entries are kept in this browser's storage so they are still here next time; clear your browser's site data to remove them.
Questions
Why does my bank's payment differ by a few cents?
Lenders round at different steps, some count interest daily rather than monthly, and many add tax or insurance to the payment. The figures here are close for a standard monthly fixed-rate loan, but your loan documents are the final word.
Can I type commas in numbers?
Yes. 1,250.50 and 1250.50 both work, and a comma followed by one or two digits, as in 12,5, is read as a decimal point.
Does it work offline?
Once the page has loaded, yes. Everything it needs is in the page itself.