Scientific calculator — online, with a simple mode and full working

Because multiplication is done before addition. This calculator reads the whole expression and applies the standard order of operations — brackets first, then powers, then multiplication and division from left to right, then addition and subtraction from left to right. So 3 × 4 is worked out first, giving 12, and 2 is added to it for 14. A basic four-function calculator, the kind on a desk, gives 20 instead, because it acts on each key as you press it and has already added 2 and 3 before it sees the ×. Neither machine is broken; they are answering different questions. If you want the 20, type (2 + 3) × 4 — brackets are the only way to override the order, and they are worth using even when they are not strictly needed, because an expression that reads unambiguously is one you can check tomorrow.

They are −9 and 9, and the difference is which operation happens first. A power binds tighter than a minus sign, so −3² means "take 3 squared, then negate it": 3² is 9, and the minus makes it −9. Writing (−3)² puts the minus inside the brackets, so the whole of −3 is squared, and a negative times a negative is positive, giving 9. This calculator follows the textbook rule, which is also the rule Python, JavaScript and every algebra course use. It is worth knowing that Excel does the opposite — =-3^2 in a spreadsheet returns 9 — which is why a figure copied out of a spreadsheet formula sometimes disagrees with the same formula typed here. Type the brackets and the ambiguity disappears.

The mode is printed next to the answer as DEG or RAD, and there is a two-button switch above the trig keys. A hidden angle mode is the most common reason a trigonometry answer comes out wrong, so it is never more than a glance away here. The quick test: in degrees, sin(30) is exactly 0.5 and sin(90) is exactly 1. In radians, sin(30) is about −0.988 and sin(90) is about 0.894. As a rule, use degrees for geometry, navigation, surveying and anything with a protractor; use radians for calculus, physics, and for checking work against a programming language, because Math.sin in every mainstream language takes radians. The inverse keys follow the same setting, so asin(1) gives 90 in DEG and 1.57079632679 — that is π/2 — in RAD.

log with no base written means base 10: log(1000) is 3, because 10 to the power 3 is 1000. ln means the natural logarithm, base e, where e is about 2.71828: ln(e) is 1, and ln(1000) is about 6.9078. The convention is not universal, which is exactly why the question keeps being asked — most calculators and most engineering and chemistry writing use log for base 10, while most pure mathematics papers and many programming libraries use log for the natural logarithm. This page follows the calculator convention. If you need a logarithm in some other base, divide: log base 2 of 64 is log(64) ÷ log(2), which is 6, and the same trick works with ln on both halves. Logs of zero and of negative numbers are refused with an explanation rather than returned as an error code, because no real power of 10 or of e ever produces them.

Both are true, and the difference is rounding for display. Computers store numbers in binary, and one tenth cannot be written exactly in binary any more than one third can be written exactly in decimal — 0.3333… never terminates. So 0.1 and 0.2 are each stored as the nearest value the machine can hold, and adding those two near-misses lands a hair above three tenths. This calculator rounds every answer to 12 significant digits before showing it, which is far enough in to hide the binary dust and far enough out to keep real precision: 1 ÷ 3 still shows as 0.333333333333, not as 0.33. The full unrounded value is what gets stored in Ans and in memory, so chaining a long calculation does not lose accuracy at every step — only the display is rounded, never the arithmetic.

It divides the number in front of it by 100, and nothing else. So 15% is 0.15, 200 × 15% is 30, and 50% + 50% is 1. This is the mathematical reading of the symbol and it composes properly with everything else on the keypad. It is not the "percent key" behaviour of a supermarket desk calculator, where 200 + 15% silently means "add fifteen percent of 200" and returns 230; here 200 + 15% is 200.15, because 15% really is 0.15. To add fifteen percent, type 200 × 1.15, or 200 + 200 × 15%. The desk-calculator shortcut guesses what you meant based on which operator came before, and a calculator that guesses is a calculator that is occasionally confidently wrong.

All the digits, a full stop for the decimal point, + − * / ^ ( ) % and !, and the letters that spell a function name — typing s-i-n-( is exactly the same as tapping the sin key. Enter or = evaluates and adds the line to the history. Backspace deletes one character. Escape clears the expression, and so does Delete when the field is not focused. You can paste an expression in from somewhere else, and thousands separators inside a number are understood, so 1,250 + 4 gives 1,254. A stray comma that is not a thousands separator is reported as an error rather than quietly ignored, because ignoring it would turn 1,250 into 250 without telling you.

Because "NaN" tells you nothing you did not already know. Every dead end here gets a sentence naming what went wrong and, where there is one place to point at, the position in the expression. Dividing by zero, taking the square root of a negative, taking a log of zero or of a negative, a factorial of a fraction or of a negative number, tan(90°), an inverse sine of anything outside −1 to 1, unbalanced brackets, and an expression that simply ends too early are each reported in their own words. Two are worth knowing about in advance: 171! overflows past the largest number a browser can hold, so 170! is the biggest factorial available; and tan(90°) is refused exactly in degrees, while in radians π/2 cannot be typed exactly, so that one comes out as an enormous number rather than an error — the message says so when it happens.

No. The parser and the arithmetic are JavaScript running in this tab; there is no server involved at any point, and the page works with the connection switched off once it has loaded. Nothing is written to your browser storage either — the history list, the memory register and the last answer live in the page, and closing or reloading the tab clears all three. That is deliberate: a calculation is finished in one sitting, so saving it buys almost nothing and would downgrade what this page can honestly promise. Like every page on this site, it does serve ads, which is explained on the privacy page.