Excel formula to calculate negative nominal rate of return from effective rate

[financialadvisor1]

I need an excel formula to calculate the negative nominal rate of return given the negative effective rate and the number of compounding periods per year. Excel's NOMINAL and NPER functions do not work when a negative rate assumption is used resulting in a #NUM! error. The context for this is that I am using <ACRONYM title=Microsoft>MS</ACRONYM> Excel to to investment analysis. I want to analyse the resulting value of an investment account balance when there is a negative effective rate and corresponding nominal rate of return (mimicing a declining value in a particular investment/account due to negative annual return on investment expressed as a negative annual effective rate of return but that is compounding monthly - and hence the need for the nominal rate and compounding periods). I need to use a calcualtion in Excel that gives me the negative nominal rate of return equivalent to the negative effective rate of return assumtion.

Please help and thank you in advance if you can solve this!<!-- google_ad_section_end --> <!-- / message --><!-- edit note -->