Too Many Arguments in Nested IF Statements starting with IFERROR

[Snake Eyes]

Greetings,
I'm trying to eliminate the "Too many arguments in this formula" but changes I have tried on my own get me either "Formulas is missing opening or closing parenthesis" or "Too Few Arguments in this formula".
Any clarity would be appreciated.
And while on this topic, is there an excel formula syntax primer that I could review that would help me to resolve seemingly simple issues like this?
Many Thanks.

=IFERROR(IF(T18="Monthly",M18*AA18/3),IF(T18="Quarterly",M18*AA18),IF(T18="Semi-Annually",M18*AA18*2),IF(T18="Annually",L18),"")

 

[Snake Eyes]

Thanks to each of you for your input here. Truly appreciated.
MEUserII and Fluff, your consensus and last code entries worked for me as did the entry from Rick Rothstein.
Rick, I'm totally unfamiliar with the SWITCH function so I'm going to have to do some studying on that and I'll also certainly look over the support article to which you linked MEUSerII.
Again, many thanks.

 

[Fluff]

Glad we could help & thanks for the feedback.