Newbie rental calculator vs PDF difference?

[Steve Fred]

Total newbie and I am sure it is something very obvious I am overlooking/ not taking account for.

I have done multiple rental calculator analysis for practice until I decide to make  the leap into the investing world.  The results on my rental calculator seem to differ than whats on the PDF ( about $10-$25).  For example- 

Rental property " A" will have my monthly income ( rental) at $3000, expenses at $2354 

Easy enough until I look at the PDF version and it reads

Monthly income-$3000, Expenses- $2377.52 

The difference in expenses is about $23 and just seeing what I am missing? Thanks a bunch everyone!