Basic Calculator
Everyday arithmetic — add, subtract, multiply and divide with chained operations, percentages, square roots, squares and reciprocals, a memory register (MC / MR / M+ / M−), and a running history tape.
Built by Suhaib Hassan. Our methodology.
Operates like a physical calculator: each operator is applied left to right as you enter it (not full algebraic order of operations) — the same convention as every handheld calculator.
Fast everyday arithmetic with a memory register and a visible history tape, so you can check your last few steps.
Calculator
Use the calculator to the left — every completed calculation appears here and in the history tape below.
History tape
Every calculation you complete, most recent first.
How the buttons work
- Chain operations: each operator applies immediately to the running total, left to right — like every physical calculator, not full algebraic PEMDAS (so 2 + 3 × 4 gives 20, not 14; use = after each step if you want to control the order yourself).
- √, x², 1/x: apply instantly to the number currently on screen.
- MC / MR / M+ / M−: clear, recall, add-to, or subtract-from the memory register.
- C clears the current entry only; AC clears everything, including memory-pending operations.
By Suhaib Hassan · Reviewed 29 September 2026 · How CalculatePilot verifies formulas →
Worked examples: keys pressed and what you see
| Task | Keys | Display |
|---|---|---|
| Chained arithmetic (left to right) | 2 + 3 × 4 = | 20 |
| Add 6% sales tax to 851 | 851 × 106 % = | 902.06 |
| 15% of 80 | 80 × 15 % = | 12 |
| 200 after a 15% discount | 200 × 85 % = | 170 |
| Square root | 144 √ | 12 |
| Square | 12 x² | 144 |
| Reciprocal | 8 1/x | 0.125 |
| Repeating decimal | 1 ÷ 3 = | 0.333333333333 |
| Binary rounding hidden | 0.1 + 0.2 = | 0.3 |
The % key divides the number on screen by 100 and nothing else, so 106 % becomes 1.06 and the multiplication does the work. Every result above was checked against the calculator's own display rules.
Memory keys step by step
Add 12.50 and 7.50 using the memory register instead of writing down a subtotal:
- Press MC to clear memory, then type 12.5 and press M+. MEM shows 12.5.
- Type 7.5 and press M+. MEM shows 20.
- Press MR to bring 20 back onto the screen and use it in the next calculation.
- Type a number and press M− to subtract it from memory.
The History tape keeps your last 50 completed calculations, newest first, and you can copy it or print it.
Keyboard shortcuts
| Key | Action |
|---|---|
| 0 to 9 and . | Type digits and the decimal point |
| + - * / | Add, subtract, multiply, divide |
| Enter or = | Equals |
| % | Percent (divide the entry by 100) |
| Backspace | Delete the last digit |
| Esc | All clear (AC) |
Display limits and error messages
- Digits: results are shown to 12 significant digits, which is why 0.1 + 0.2 reads 0.3 and 1 ÷ 3 reads 0.333333333333.
- Very large or small: numbers of 1e15 or more, and non-zero values below 1e-9, switch to exponent form such as 1.000000e+16.
- Division by zero: 1 ÷ 0 = shows Error: undefined, and 1/x on 0 shows Error: div by 0.
- Negative square root: shows Error: negative. Press AC to start again.
Need brackets or exponents? Use the Scientific Calculator, which follows the order of operations. For a percentage of a number or a percent change, try the Percentage Calculator.
Frequently asked questions
Why does 2 + 3 × 4 give 20 instead of 14?
Simple calculators evaluate strictly left to right as you press keys — 2+3 is computed as soon as × is pressed (=5), then 5×4=20. Scientific calculators and algebra follow order of operations (PEMDAS) instead, which would give 2+(3×4)=14. Use our Scientific Calculator for expression-based PEMDAS evaluation.
What does the % key do?
It divides the number currently on screen by 100 — so 50 % becomes 0.5, ready to use in a further calculation (e.g. for "20 × 15 %" to find 15% of 20).
What's the difference between C and AC?
C (Clear) resets only the number you're currently typing, keeping any pending operation and running total. AC (All Clear) resets everything back to zero, including memory-pending calculations (but not the M register).
Can I use negative numbers and decimals?
Yes — use ± to flip the sign of the current entry, and the decimal point key for fractional values, exactly as on a physical calculator.
How precise is the arithmetic?
It uses IEEE 754 double-precision floating point (about 15–17 significant decimal digits) — the same standard used by virtually all calculators, spreadsheets and programming languages.
Does this online calculator have memory and history?
Yes. MC, MR, M+ and M− give you a memory register shown as MEM, and the History tape lists your last 50 completed calculations. You can copy the history or print it.
How do I add or subtract a percentage on a calculator?
Type the amount, press ×, type 100 plus or minus the percentage, then press % and =. For example 851 × 106 % = gives 902.06 (6% added) and 200 × 85 % = gives 170 (15% off).
What keyboard shortcuts does it support?
Digits and the decimal point, + - * /, Enter or = for equals, % for percent, Backspace to delete a digit and Esc for all clear.
Why does 0.1 + 0.2 show 0.3 here?
Computers store 0.1 and 0.2 in binary, so the raw sum is 0.30000000000000004. The display rounds to 12 significant digits, so you see 0.3.
What do the error messages mean?
Error: undefined appears after dividing by zero, Error: div by 0 when you press 1/x on zero, and Error: negative when you take the square root of a negative number. Press AC to clear it.
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