Basic Calculator
A desk calculator that never drifts: exact decimals, % that works, and a paper tape.
Keyboard: digits, + − * /, Enter, %, r √, n ±, Backspace, Del clear entry, Esc clear all.
Paper tape
Finished calculations appear here. Click a number to correct it.
About the Basic Calculator
A fast everyday calculator for sums, bills and quick checks. It calculates with exact fractions instead of the binary floating point most calculators use, so 0.1 + 0.2 is exactly 0.3, 1 ÷ 3 × 3 is exactly 1, and a long column of rupees and paise adds up to the paisa.
The % key works like a desk calculator — 200 + 10% = 220 and 200 − 10% = 180 — and there are memory keys, a square root and a sign change. Every finished calculation goes onto a paper tape: you can correct any number on it and the totals update, give a line a label, and copy, print or download the tape as a CSV file for a spreadsheet. Digits are grouped the Indian way (1,00,000) or the international way (100,000).
How to use it
- Click the keys or type on your keyboard: digits,
+ − * /,Enteror=for equals,%,Backspaceto delete a digit,Deleteto clear the entry andEscto clear everything.rtakes a square root andnchanges the sign. - For a percentage, type the number and press %:
200 + 10 %shows 20 straight away, and=gives 220. - Press
=again to repeat the last operation (2 + 3 = 5, = 8, = 11). After a result, an operator carries on from it and a digit starts a new calculation. - On the paper tape, click any number to correct it — results that depend on it update too. Use Copy, CSV or Print to keep the tape. It is saved in this browser until you clear it.
- Choose Indian or international digit grouping, and whether × and ÷ come before + and − (standard) or the keys are worked left to right like many desk calculators.
Examples
1500 + 18 % =
1,770
18% of 1,500 is 270, added on. 1500 − 18 % gives 1,230, and 1500 × 18 % gives 270.
0.1 + 0.2 =
0.3
Many calculators built on binary floating point give 0.30000000000000004 here.
2 + 3 × 4 =
14 (standard) · 20 (left to right)
100 × 2 = = =
200, 400, 800
Common uses
- Adding up bills, receipts and shopping lists, then copying the tape into a spreadsheet.
- Adding GST or taking off a discount with the % key.
- Checking a total line by line and fixing a mistyped entry without starting over.
How the % key works
- a + b% adds b percent of a: 200 + 10% = 200 + 20 = 220.
- a − b% takes b percent of a away: 200 − 10% = 180.
- a × b% gives b percent of a: 200 × 10% = 20.
- a ÷ b% divides by b/100: 200 ÷ 10% = 2,000.
- b% on its own is b/100: 10% = 0.1.
In a longer calculation, a percentage after + or − is taken of everything before it: 50 + 2 × 3 + 10% = 56 + 5.6 = 61.6.
Why the answers are exact
Most calculators and programming languages store numbers in binary, where 0.1 cannot be written exactly, so tiny errors creep in (0.1 + 0.2 = 0.30000000000000004). This calculator keeps every number as an exact fraction of whole numbers, so adding, subtracting, multiplying and dividing never lose anything. Results are shown rounded to 15 significant digits; the full value is kept for the next step, which is why 1 ÷ 3 × 3 comes back to exactly 1. Square roots of non-perfect squares are irrational and are computed to 40 significant digits.
Standard order or left to right?
In standard order (the default), × and ÷ are done before + and −, as in maths and on phone calculators: 2 + 3 × 4 = 14. Many desk and office calculators instead work each key immediately, left to right: 2 + 3 = 5, then × 4 = 20. Pick whichever matches the calculator you are used to; each calculation on the tape remembers the order it used.
Limitations
- Entries can have up to 15 digits; results are shown to 15 significant digits, and larger or smaller numbers in scientific notation (1.5e+20).
- There are no brackets or functions here — use the scientific calculator for those.
- The tape is stored only in this browser (up to 200 calculations). Clearing site data removes it.
Privacy
Everything happens in your browser. What you enter or open here is not uploaded or stored by MySmartCoPilot.
Frequently asked questions
Why does this calculator say 0.1 + 0.2 = 0.3 when some apps show 0.30000000000000004?
Those apps use binary floating-point numbers, which cannot store 0.1 exactly. This calculator works with exact fractions, so decimal sums come out exactly as on paper.
How do I add a percentage, such as 18% GST?
Type the amount, press +, type 18 and press %, then =. 1,000 + 18% = 1,180. To take a percentage off, use − instead: 1,000 − 18% = 820. For the price before GST was added, divide by 1.18 (or use the GST calculator).
Can I use my keyboard?
Yes. Digits, the decimal point, + − * /, Enter or =, %, Backspace, Delete (clear entry) and Esc (clear all) all work, plus r for square root and n for ±. Digit-group commas are added for you, so typing a comma does nothing — use a full stop for decimals (the decimal key of a numeric keypad works too). You can also paste a number such as 1,23,456.50; a decimal comma such as 1.234,56 is refused rather than misread.
How do I correct a mistake on the tape?
Click the number on the tape, type the right value and press Enter. The result of that calculation updates, and so does any later calculation that carried on from it.
What do MC, MR, M+ and M− do?
They use a memory that holds one number. M+ adds the number on the display to the memory, M− subtracts it, MR puts the memory on the display and MC clears it. An M on the display shows that the memory is not zero.