Add two or more positive or negative numbers with exact decimal handling, or find a missing addend from a known total. Review the sum, running totals, and calculation formula.
Addition Calculator
Enter numbers
The total that all addends must equal.
Advanced options
Your settings stay in this browser and are not sent anywhere.
Result
Enter at least two valid numbers to calculate.
Value composition
Bars are proportional and intended for visualization; use the displayed values for exact results.
Detailed breakdown
| Item | Operation or detail | Result |
|---|
Formula and Calculation
General formula
Substitution
Calculation
Exact result
Displayed result
How to Use This Tool
- Choose whether to add numbers or find a missing addend.
- Enter each value, including a minus sign for negative numbers.
- Add or remove rows as needed.
- Select how many decimal places to display.
- Press Calculate, then review the breakdown and formula.
- Copy, share, print, or download the result when needed.
How the Calculation Works
In addition mode, the calculator combines every entered value in order. Positive numbers increase the running total; negative numbers decrease it.
In missing-addend mode, the known addends are first summed and then subtracted from the target total.
Formula Explanation
For ordinary addition, S = a₁ + a₂ + … + aₙ, where each a is an addend and n is the number of values.
For a missing value, x = T − (a₁ + a₂ + … + aₙ), where T is the target total.
Worked Example
Suppose the values are 1,250.75, 349.20, −99.95, and 18. Their sum is 1,518 because 1,250.75 + 349.20 − 99.95 + 18 = 1,518.
If the target were 2,000, the missing addend would be 482.
Understanding the Results
The main answer is the exact sum or missing addend, formatted using your selected precision. Supporting results show count, positive or known subtotal, and average or target.
The detailed schedule shows how each input changes the running total.
Common Mistakes
- Omitting a minus sign from a value that should be subtracted.
- Using a comma as a decimal separator instead of a period.
- Entering incorrectly grouped thousands separators.
- Rounding each addend before calculating.
- Confusing the target total with a known addend.
Technical Notes
This tool aligns decimal places and calculates with integer-based decimal arithmetic, avoiding common binary floating-point artifacts such as 0.1 + 0.2 displaying as 0.30000000000000004. Inputs may contain up to 15 integer digits and 12 decimal places. Display rounding is applied only after the exact total is calculated.
Frequently Asked Questions
Can I add negative numbers?
Yes. Include a minus sign before any negative addend, such as −12.5.
Can I use decimals?
Yes. Use a period as the decimal separator. Up to 12 decimal places are supported.
Why does the displayed answer have trailing zeros?
A fixed precision selection deliberately pads the result. Choose Auto to remove unnecessary trailing zeros.
How many numbers can I add?
You can use between 2 and 100 addends in one calculation.
What is a missing addend?
It is the number that must be added to the known values to reach the target total.
Are commas allowed?
Yes, when they are valid thousands separators, as in 12,500.75. Use a period for decimals.
Are my values sent anywhere?
No. Calculations stay in your browser. If remembering is enabled, settings are stored only on this device.
Important Note
Check source values, signs, and required rounding rules before relying on a result for financial, scientific, engineering, or other consequential work. This calculator is a general arithmetic aid, not professional certification.