reporting services - Get the value from previous row in SSRS -

i want show 2 columns on report. 1 "amount", field sql server table, , 1 "balance", column derived in report. first value of "balance" same "amount". since 2nd row, value of "balance" sum of value previous row of "balance" , current row of "amount". can imagine how can achieve if using excel. tried use function "previous", i'm not sure how previous value of "balance", because it's not field in sql server table.

if want sum current row previous row may using runningvalue . using runnningvalue can sum of current row previous one. here set expression balance field

=runningvalue(fields!amount.value,sum,nothing)