Currently we are having (Opportunities(won)last 12 months) field which is of Roll-up summary data type , updating the count in this field on criteria when
Close date of opportunity >= (some date).
There is no way to give Value as TODAY or any inbuilt value. Instead of roll-up summary type can we use formula based field to count the closed won opportunity in account and update the field.
If possible could you please provide us the formula..