Free · Arithmetic
Signed Subtraction & Missing-Value Calculator
Subtract integers or decimals, including negative numbers, or recover either missing input from the difference.
- Formula & worked example
- Private in your browser
- No signup
Calculator inputs
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How to use this calculator
- Enter the known values in the units shown. Results update as you type.
- Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
- Use the worked example to check the method. Reset restores the starting fields.
Private by default
Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.
Formula and method
12.5 − (−3.25) = 15.75. If the difference is 15.75 and the first number is 12.5, the second number is −3.25.
Difference = first number − second number
Worked example
Enter these known values and leave the other values blank.
- First number — minuend
- 12.5
- Number subtracted — subtrahend
- -3.25
- Difference
- 15.75
Assumptions and limitations
- Values are finite real numbers, with calculations using 64 significant digits. Very long inputs can exceed that working precision.
- Enter a negative number with its minus sign. The order matters: reversing the two inputs reverses the sign of the difference.
Common questions
Can I find a missing first number?
Yes. Enter the second number and difference; the first equals their sum.
Why does subtracting a negative increase the result?
Subtracting −b is equivalent to adding b.
References
The calculation equations, inverse formulas, units, and input rules were imported from this source. Bookify provides the interface and equation solver.