下表列出了所有Tcl語言支援的算術運算子。假設變數A=10，變數B=20，則：
| 運算子 | 描述 | 例子 |
|---|---|---|
| + | 兩個數相加 | A + B = 30 |
| - | 第一個運算元減去第二個運算元 | A - B = -10 |
| * | 兩個運算元相乘 | A * B = 200 |
| / | 分子(B)除以分母(A) | B / A = 2 |
| % | 模運算和整數除法後的餘數 | B % A = 0 |
試試下面的例子就明白了所有Tcl語言中可用的算術運算子：
#!/usr/bin/tclsh set a 21 set b 10 set c [expr $a + $b] puts "Line 1 - Value of c is $c\n" set c [expr $a - $b] puts "Line 2 - Value of c is $c\n" set c [expr $a * $b] puts "Line 3 - Value of c is $c\n" set c [expr $a / $b] puts "Line 4 - Value of c is $c\n" set c [expr $a % $b] puts "Line 5 - Value of c is $c\n"
當編譯和執行上面的程式，它會產生以下結果：
Line 1 - Value of c is 31 Line 2 - Value of c is 11 Line 3 - Value of c is 210 Line 4 - Value of c is 2 Line 5 - Value of c is 1