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How to use this online calculator
This online calculator behaves like the pocket calculator in your drawer, with a few things that drawer calculator never had: a tape of everything you worked out, keys you can hit with a keyboard, and a switch for how it orders the sums.
- Tap the keys or type on your keyboard. Digits,
+ − * /,%, Enter for equals, Backspace to delete one digit. - Use C to wipe the number you are typing and AC to start over. AC leaves the memory alone.
- Press = again to repeat the last operation. Tap any line on the history tape to bring its result back.
- Under the keys, choose Order of operations (multiply and divide first) or Left to right (the way a basic pocket calculator works).
- When you are done, copy the whole tape or download it as a .txt file. Handy for a shopping list, a quick invoice check or a note for your accountant.
Everything runs in your browser. Nothing you type is sent anywhere, and the tape is stored only on your own device until you press Clear.
How does the percent key on a calculator work?
The % key does not mean the same thing after every operator, which is why it confuses people. After a plus or minus it works out that percentage of the number before it and then adds or subtracts it. After a times or divide it just divides your number by 100.
| Keys | Result | What happened |
|---|---|---|
| 200 + 10% = | 220 | 10% of 200 is 20, added to 200 |
| 200 − 10% = | 180 | 20 taken off 200 |
| 200 × 10% = | 20 | 10% became 0.1, then 200 × 0.1 |
| 1,000 − 15% = | 850 | a 15% discount |
| 80 + 25% = | 100 | 25% of 80 is 20 |
| 50 % | 0.5 | on its own, divide by 100 |
One trap: percentages stack on the new total, not the original. 100 + 10% + 10% is 121, not 120, because the second 10% is taken from 110. To find 15% of 80, type 80 × 15% and you get 12. To go the other way and find what percent 12 is of 80, divide: 12 ÷ 80 = 0.15, which is 15%.
Order of operations or left to right?
Type 2 + 3 × 4 on a phone and you get 14. Type it on a cheap pocket calculator and you get 20. Neither is broken. The phone multiplies first, the pocket calculator does each step as you press it, so it works out (2 + 3) × 4.
| Sum | Order of operations | Left to right |
|---|---|---|
| 2 + 3 × 4 | 14 | 20 |
| 15 + 5 × 2 | 25 | 40 |
| 3 × 1.20 + 2 × 0.75 | 5.10 | 4.20 |
| 100 − 50 ÷ 5 × 2 | 80 | 20 |
The third row is a real shopping sum: three items at $1.20 and two at $0.75 cost $5.10. Left to right gives $4.20, which is simply wrong for that question. Keep the default unless you are checking a figure against a pocket calculator that works the old way.
How do I repeat the last calculation?
Press = again. The calculator remembers the last operator and the last number and applies them to the result. After 2 + 3 = you see 5, then 8, then 11. This is the quickest way to compound a number: 1000 × 1.075 = gives 1,075, and pressing = twice more gives 1,155.625 and 1,242.296875, which is a 7.5% increase applied three times. You can also type a fresh number and press =: after the sum above, typing 7 and pressing = gives 10.
Memory keys: M+, M−, MR and MC
Use memory as a running total while you do other sums. M+ adds the number on the display, M− subtracts it, MR recalls it and MC clears it. A small M appears on the display when something is stored. Example: type 12.50, M+, then 8.25, M+, then 3.10, M−. MR now shows 17.65. The memory survives AC and a page reload on the same device.
Adding or removing tax with TAX+ and TAX−
Enter your rate once in the Tax rate box (it is remembered), type a price and press TAX+ to add the tax or TAX− to take it out of a price that already includes it. Results are rounded to cents unless you untick that option.
| Price | Rate | Key | Result |
|---|---|---|---|
| $49.99 | 8% | TAX+ | $53.99 |
| $120.00 | 8.25% | TAX+ | $129.90 |
| $19.99 | 10% | TAX+ | $21.99 |
| $108.00 | 8% | TAX− | $100.00 |
TAX− divides by 1.08, it does not subtract 8%. Taking 8% off $108 would leave $99.36, which is not the original price. For a dedicated tool with invoices and different tax styles, the VAT calculator is better; this is for the quick check at the till.
Why 0.1 + 0.2 shows 0.3 here
Computers normally store numbers in binary, and 0.1 has no exact binary form, so many tools print 0.30000000000000004. This calculator does decimal arithmetic instead, so the sums you do by hand come out the way you expect. Division is rounded sensibly: 1 ÷ 3 shows 0.333333333333, and multiplying that back by 3 gives 1. The limits are 15 digits when typing, and results longer than 15 digits switch to scientific notation such as 1e+15. For roots, powers and trigonometry use the scientific calculator linked under the keys.
Keyboard shortcuts
| Key | Does |
|---|---|
| 0–9, . or , | digits and decimal point |
| + − * / | operators (x also multiplies) |
| Enter or = | equals, and repeat on a second press |
| Backspace | delete the last digit |
| Delete | clear the entry (C) |
| Esc | clear everything (AC) |
| Ctrl+C / Ctrl+V | copy the display / paste a number |
Frequently asked questions
How does the percent key work on a calculator?
After + or −, the % key turns the number you typed into that percentage of the number before it, so 200 + 10% = 220 and 200 − 10% = 180. After × or ÷ it simply divides by 100, so 200 × 10% = 20.
Why does 2 + 3 × 4 give 14 on one calculator and 20 on another?
Scientific and phone calculators multiply first and get 14. Basic pocket calculators work strictly left to right, so (2 + 3) × 4 = 20. This page does both: pick Order of operations or Left to right under the keys.
How do I repeat the last calculation with the equals key?
Press = again. After 2 + 3 = 5, a second press gives 8 and a third gives 11, because the calculator repeats + 3. Typing 7 and pressing = then gives 10.
How do I add sales tax to a price on a calculator?
Set the rate once (for example 8), type the price and press TAX+. For $49.99 at 8% you get $53.99, and TAX− on $53.99 takes you back to $49.99.
Why does 0.1 + 0.2 equal 0.3 here when other tools show 0.30000000000000004?
Most programs use binary floating point, which cannot store 0.1 exactly. This calculator does its arithmetic in decimal, so 0.1 + 0.2 is exactly 0.3 and 1.1 × 1.1 is exactly 1.21.
How do the memory keys M+, M−, MR and MC work?
M+ adds the number on the display to memory, M− subtracts it, MR brings it back and MC clears it. Entering 12.50 M+, 8.25 M+ and 3.10 M− and then pressing MR shows 17.65.
Can I type with my keyboard, and is my history saved?
Yes. Digits, + − * /, %, Enter, Backspace, Delete and Esc all work. The tape is stored only in your browser on this device, and the Clear button wipes it.
What happens if I divide by zero?
The display shows Cannot divide by zero instead of a number. Press AC or start typing a new number and the calculator is ready again; the memory is not touched.