Total for Calculated Field not adding up

System generated ageing report if a invoice is 0-30 days, it pull the invoice amount in the respective column and a 0 in other column. I need to see each supplier has how many invoice is overdue 30 days, 60 days etc.
HOwever, due to the 0, Pivot table would include it when i subtotal using Count. Hence i insert calculated field. which is =if(' 30 Days"=0,0,1). However, when i use the sum subtotal for the Calculated field, it keep showing 1 despite having more than one's 1 above. Why is this so?