Count Month value per record with MS Access

[shahed1985]

I create a MS access database with two table

Main_table : ID_number, Student_name, Class

Collection_Table : Collection_Date, ID_number,
Student_name, Class, PaidForMonth,Installment, PaidAmount.


Collection_Table relation with main_table.

ID_number, Student_name, Class

PaidForMonth = is a list of month a year.(July to June)
(can choice multiple value in a column)

I use a count(PaidForMonth) formula in data entry form which is count only collection_date Example: Collection date: 08/08/2015 "PaidForMonth": Jul, Aug,. in the column "Installment" it show : 2
but but in the next collection date in the "Installment" column shows with previous count 2 + 2 (today's value Sept, Oct). But I want to count today's "PaidForMonth" values 2.

I think everyone can understand my problem. Please solve my problem.

[jforbes]

What code are you using?