How to Perform Basic Math (Add, Subtract, Multiply, Divide) in Batch Script

Performing simple mathematical calculations is a fundamental requirement for many scripts. You might need to increment a counter, calculate an offset, or determine a total. The standard way to handle math in a Windows Batch script is with the SET command, used with its special /A (Arithmetic) switch.

This guide will teach you the syntax of SET /A and show you how to perform all the basic arithmetic operations. You will also learn about its integer-only limitation and how to control the order of operations with parentheses.

The Core Command: SET /A

The SET /A command tells the command processor to treat the string that follows as an Arithmetic expression. It can evaluate the expression and, optionally, assign the result to a variable.

Syntax: SET /A "VariableName = expression"

• VariableName =: This part is optional. If you include it, the result of the calculation is stored in VariableName. If you omit it, the result is simply printed to the command line.
• expression: The mathematical formula you want to evaluate (e.g., 5 + 3).

Basic Arithmetic Operators

The SET /A command supports all the standard operators you would expect:

Operator	Description	Example
+	Addition	5 + 3
-	Subtraction	10 - 4
*	Multiplication	6 * 7
/	Division	20 / 5
%%	Modulo (Remainder)	13 %% 5

Basic Examples of Math Operations

For these examples, we will store the result in a variable and then ECHO it.

Addition (+)

@ECHO OFF
SET "Apples=5"
SET "Oranges=10"

SET /A "TotalFruit = %Apples% + %Oranges%"
ECHO Total fruit: %TotalFruit%

Output:

Total fruit: 15

Subtraction (-)

@ECHO OFF
SET "TotalItems=100"
SET "ItemsUsed=42"

SET /A "ItemsLeft = %TotalItems% - %ItemsUsed%"
ECHO Items left: %ItemsLeft%

Output:

Items left: 58

Multiplication (*)

@ECHO OFF
SET "Price=10"
SET "Quantity=7"

SET /A "TotalCost = %Price% * %Quantity%"
ECHO Total cost: $%TotalCost%

Output:

Total cost: $70

Division (/)

This is where you must be careful. SET /A only performs integer division.

@ECHO OFF
SET /A "Result = 10 / 3"
ECHO 10 divided by 3 is: %Result%

Output:

10 divided by 3 is: 3

note

The 0.333... fractional part is completely discarded.

Combining Operations and Using Parentheses

The SET /A command understands the standard mathematical order of operations (multiplication and division are performed before addition and subtraction). You can use parentheses () to control the order explicitly.

@ECHO OFF
ECHO --- Calculating with and without parentheses ---

REM This will calculate 5 * 10 first. (2 + 50) = 52
SET /A "Result1 = 2 + 5 * 10"
ECHO 2 + 5 * 10 = %Result1%

REM The parentheses force 2 + 5 to be calculated first. (7 * 10) = 70
SET /A "Result2 = (2 + 5) * 10"
ECHO (2 + 5) * 10 = %Result2%

Common Pitfalls and How to Solve Them

The Integer-Only Limitation

This is the single biggest limitation of SET /A. It cannot handle decimals or floating-point numbers.

• 10 / 4 will result in 2, not 2.5.
• SET /A "Value = 99.5" will cause an error.

Solution: For any math that requires decimal precision, you must delegate the calculation to a more powerful tool like PowerShell.

FOR /F %%N IN ('powershell -Command "10 / 4"') DO SET "Result=%%N"
ECHO The precise result is: %Result%

This PowerShell one-liner correctly returns 2.5.

Division by Zero

If your script attempts to divide by a variable that contains 0, it will crash with a "Divide by zero error."

Solution: Always check if your denominator is zero before performing a division.

IF %TotalItems% EQU 0 (
    ECHO Cannot divide by zero.
) ELSE (
    SET /A "Average = %TotalCost% / %TotalItems%"
    ECHO The average cost is: %Average%
)

Practical Example: A Simple File Counter

This script uses SET /A to increment a counter inside a FOR loop to count the number of text files in a directory.

@ECHO OFF
SETLOCAL ENABLEDELAYEDEXPANSION

SET "count=0"

ECHO --- Counting .txt files ---
FOR %%F IN (*.txt) DO (
    REM Increment the counter by 1 for each file found.
    SET /A "count+=1"
)

ECHO Found !count! text files in this directory.

ENDLOCAL

note

DelayedExpansion (!count!) is required here to correctly read the changing value of the count variable inside the loop.

Conclusion

The SET /A command is the simple and effective built-in tool for performing integer arithmetic in a batch script.

Key takeaways:

• The core syntax is SET /A "Var = expression".
• It supports all basic operators: +, -, *, /, and %% (modulo).
• It is strictly for integers and will truncate any decimal results from division.
• For floating-point math, you must use a more powerful tool like PowerShell.
• Always check for a division by zero to prevent your script from crashing.