"George" wrote:
The amount to this formula should be 363.04

What value do you get instead?

=(C4*2%+(C415651.89)*(C4-15651.89)*5%)
where C4 = 16651.89

That should result in about 383.04.

I need to find 2% of C4 up to 15651.89 and
anything over that (difference) at 5%

Then you have the wrong formula. Ostensibly, you want:

=min(C4,15651.89)*2% + max(0,C4-15651.89)*5%

That does indeed result in about 363.04.

Notice that I say "about" this or that. The actual value is 363.0378. It
would behoove you to use ROUND to avoid surprises in later calculations.
Assuming that you have ROUND'd C4, the above formula should be:

=round(min(C4,15651.89)*2% + max(0,C4-15651.89)*5%, 2)

Alternatively:

=round(C4*2% + max(0,C4-15651.89)*3%, 2)

where 3% is 5% - 2%.