Add two finite real numbers, including negatives, decimals, and scientific notation, and optionally save recent sums.
Last updated: August 2026 | By Summa Calculator
First number is required.
Addition combines two quantities into a sum. For numbers a and b, the operation is written a + b.
Addition is commutative, so a + b = b + a. It is also associative, so (a + b) + c = a + (b + c). Zero is the additive identity because a + 0 = a.
Those properties can make mental addition easier because terms can be reordered or regrouped without changing the total.
If both numbers have the same sign, add their magnitudes and keep that sign. If their signs differ, subtract the smaller magnitude from the larger magnitude and keep the sign of the number with the larger magnitude.
Decimal values follow the same addition rules as other real numbers. For manual addition, matching decimal places helps keep place values aligned.
This calculator uses JavaScript numeric arithmetic, so some decimal values cannot be represented exactly in binary. The displayed sum is rounded for readability rather than presented as arbitrary-precision arithmetic.
What numbers can I enter?
Finite real numbers written as decimals or scientific notation are supported, including zero and negative values.
What happens if the sum is too large?
If two finite inputs overflow JavaScript’s numeric range when added, the calculator reports an error instead of displaying a false result.
Why might a decimal be rounded?
JavaScript numbers use binary floating-point arithmetic. The calculator rounds displayed results to at most eight decimal places.
What does Save do?
Save keeps up to five recent valid sums in the current component state so you can compare calculations on the page.
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