"Crackles McFarly" wrote...
"Harlan Grove" sayd the following:
....
Next assuming 10% effective annual.

FV: =FV(NOMINAL(10%,12)/12,300,-100,-500) returns 128,749.84.

That 2nd formula gives an error of "#NAME?"

Which means you don't have the Analysis ToolPak loaded. Fine, use

=FV(1.1^(1/12)-1,300,-100,-500)

And I am assuming a continual interest rate while placing exactly $100
in at the start of the month [or end if it makes this easier?]

Yup, 10% effective annual interest rate, assuming you mean continuOUS
COMPOUNDING since 'continual interest' has no meaning in Interest Theory,
and could only be interpreted colloquially as meaning your mutual fund
continues to pay you interest rather than becoming insolvent or taking the
money and running away.