Most daily arithmetic does not need a spreadsheet or a scientific calculator: splitting a restaurant bill, checking a discount, adding up a shopping list, converting a quantity in a recipe. This calculator covers exactly that with a large keypad that works with a mouse, a touchscreen or a stylus, and it opens instantly with no sign-up.

The keypad, key by key

• 0 to 9 and . build a number. A leading decimal point starts the number as 0.
• +, −, ×, ÷ choose the operation to apply to the number you are typing next.
• ＝ completes the pending operation and shows the answer.
• C clears everything and returns the display to 0.
• +/− flips the sign of the number currently on the display.
• % divides the displayed number by 100, turning 25 into 0.25.

Working through an example

To total a bill of 48.50, 32.25 and 17.80, press 4 8 . 5 0 +, then 3 2 . 2 5 +. At this point the display shows the running total of 80.75. Then press 1 7 . 8 0 ＝ for 98.55. Chained operations are evaluated as you go, from left to right, so a long row of additions works the way a pocket calculator does.

Splitting that bill four ways: press C, type 98.55, press ÷, 4, ＝ and read 24.6375. Round to the nearest cent yourself, 24.64, because the calculator shows the number without applying currency rounding.

Order of operations: read this once

This is a sequential calculator, not an expression calculator. If you press 2 + 3 × 4 ＝ it finishes 2 + 3 first and then multiplies by 4, giving 20, not the 14 that algebra rules would give. Most basic pocket calculators behave this way. When a sum mixes addition with multiplication or division, either work the multiplication first and then add, or use the Scientific Calculator, which accepts brackets and evaluates a whole expression at once.

Percentages

The % key converts the number on the display to a fraction of one hundred, nothing more. To find 15 percent of 240, press 2 4 0 ×, then 1 5 % (which turns the display into 0.15), then ＝ for 36. To add 15 percent tax to a price of 240, multiply by 1.15 instead: 2 4 0 × 1 . 1 5 ＝ gives 276. For percentage change, markup and "what percent is X of Y" questions, the dedicated Percentage Calculator on this site is easier.

Precision and rounding

Calculators use binary floating-point numbers, which cannot store some decimals exactly. The well-known example is 0.1 + 0.2, which a computer stores as 0.30000000000000004. To hide that noise, this calculator rounds each result to ten decimal places and drops trailing zeros, so you see 0.3. For money, ten places is more than enough. For scientific work where tiny differences matter, treat the last digit with caution.

Division by zero and other errors

Dividing by zero is undefined, and the display shows Error instead of a number. Press C to start again. If you press an operator twice in a row, the second one replaces the first, so slips like 5 + × 3 do no harm.

Everyday uses

• Checking a shop receipt or a utility bill total.
• Working out unit prices, such as cost per kilogram or per litre.
• Scaling a recipe up or down by multiplying each quantity.
• Quick homework checks for primary and secondary school arithmetic.
• Estimating a tip or splitting expenses between friends.

Keeping your numbers private

Every calculation happens in your browser. The numbers you type are not stored on a server and are cleared when you close or reload the page.

Sanity-check your answers

Good calculator habits matter more than the keypad. Before you press equals, make a rough estimate in your head: 49 × 21 is close to 50 × 20, so the answer should be near 1,000, and the calculator's 1,029 fits. If a result is wildly off, you probably pressed a wrong key or entered a number twice. Re-enter the calculation from C rather than trying to repair it.

Everyday percentage patterns

• Discount: a shirt costs 80 and is 25 percent off. Compute 80 × 0.75 to get the sale price of 60, rather than working out 25 percent and subtracting.
• Tax added: a 120 bill plus 5 percent tax is 120 × 1.05 = 126.
• Percentage change: a price rising from 50 to 60 is a change of 10, and 10 ÷ 50 = 0.2, which is 20 percent. Always divide by the starting value.
• Unit price: a 750 g pack for 3.90 costs 3.90 ÷ 750 = 0.0052 per gram, or 5.20 per kilogram after multiplying by 1,000. Comparing unit prices is the fastest way to see which pack is the better deal.

A common mistake is to treat a 20 percent increase followed by a 20 percent decrease as a return to the start. It is not: 100 becomes 120, and 20 percent off 120 is 96.

Frequently asked questions