I'm getting an error saying I've entered too many arguments in excel

I am trying to do a calculation on the fiscal year expenditure based on whether the contract ends within the fiscal year or if it starts within the fiscal year, then determine the number of months and multiply it by the monthly rate but I keep getting an error saying "too many arguments" I don't think I'm at 64 arguments but I'm a sometimes excel user here is the nested IF statement:

=IF([@[Contract End Date]]>=43190,[@[Annual Rate]],
IF([@[Role Start Date]]<42826,(((YEAR("2018-3-31")-YEAR([@[Role Start Date]]))*12+MONTH("2018-3-31")-MONTH([@[Role Start Date]]))*[@[Monthly Rate]])),
IF([@[Contract End Date]]<43190,(((YEAR([@[Contract End Date]])-YEAR("2017-4-1"))*12+MONTH([@[Contract End Date]])-MONTH("2017-4-1"))*[@[Monthly Rate]])))