Addition, Sum Calculator
Online adding calculator: calculate the sum of two numbers. Enter the first number, enter the second number and press = to get the sum result. Whole numbers, decimals and negative numbers all work, and everything runs locally in your browser.
Enter the first number
Type the first addend — a whole number (12), a decimal (0.1) or a negative number (-7.5). Scientific notation such as 1e21 also works.
Enter the second number
Type the second addend in the "+ Enter second number" field. The two values are what get added — subtraction is just adding a negative number, e.g. 9 + (-4).
Press = and read the sum
The sum result appears in the result field, e.g. 2 + 3 = 5. Press C to clear both inputs and the result and start over.
How addition works here
- What is the addition formula?
- The sum is simply c = a + b, where a and b are the two numbers you enter. For example 12 + 30 = 42, and -7.5 + 2.5 = -5.
- Why does 0.1 + 0.2 show 0.30000000000000004 instead of 0.3?
- This calculator keeps the full IEEE-754 double-precision result, the same arithmetic every JavaScript engine and spreadsheet uses. 0.1 and 0.2 cannot be stored exactly in binary floating point, so their stored values add to 0.30000000000000004 — an exact answer, not a bug or a rounding error.
- What happens with very large numbers?
- Beyond 2^53 (9007199254740992) double precision cannot represent every integer, so e.g. 9007199254740993 + 0 reads 9007199254740992. Past about 1.8e308 the sum overflows and the result field shows Infinity — for example 1e308 + 1e308 = Infinity.
- Can I add negative numbers and scientific notation?
- Yes. -7.5 + 2.5 gives -5, and 1e21 + 1 gives 1e+21 (adding 1 to a value that large changes nothing at double precision, and large magnitudes display in exponential form).
- What if I press = with an empty field?
- The calculator shows an in-app error telling you which number is missing, and any previous result is cleared so a stale sum can never be mistaken for the answer to your latest input.
Privacy: every calculation runs in your browser tab — no value you type is sent anywhere. Results are IEEE-754 double-precision sums, identical to what a JavaScript expression a + b evaluates to.