Wrong tax calculation?

I am single and have a fairly simple income composition. The taxable income is $124,028. last year (line 15 on Form 1040), according to TCW, the tax should be:

 

$124,028*0.24 - $5979 = $23787.

 

Yet Turbox form generated form says the tax should be $23,601. (line 16 on Form 1040)

 

Why is the difference? Am I missing anything here?

 

Many thanks.