Excel is not adding correctly

[Mine6m]

 

[#2]

Please help, this means it will offset the others after it. It suppose to be 1,663.56.

[#3]

you say "suppose to be" but excel uses the full number which means 1317.944 + 345.624 add to 1663.568 which is clearly much closer to 1663.57
I don't know what your actual numbers are but if you don't want excel to consider any additional decimal places you need to use a function like ROUND to force the output in that cell to be rounded off to a specific number of digits.
Alternatively, although i do NOT recommend it, you can force the whole sheet to use precision based on the cells display setting in OPTIONS - ADVANCED - check box for "Set precision as displayed"

[#4]

@mtarler 

thank you for the response, I’m new to excel, and I really don’t know how the numbers work. I did not know that it added the thousandths place.