Hi there!

I've been asked to restrict the valid Close Dates for Opporunities to the last day of the month when the Stage is not Closed Won/Lost.

I've found a fromula that does a great job restricting the dates in general, but I can't figure out how to add the additional condition that it should only apply the date limitation when the Opportunity is in certain stages.

IF( 
    MONTH( CloseDate ) = 12,
    DATE( YEAR( CloseDate ) + 1, 1, 1 ),
    DATE( YEAR( CloseDate ), MONTH( CloseDate ) + 1, 1 )
  ) - 1 
)

Any help/insight would be greatly appreciated!