Interest Calculation Process in SAP

First the program identifies the items on which Interest calculation is to be calculated according to the rules defined in the interest indicator, and any additional specifications you make when executing the program. The rules you enter determine the items and transaction for which Interest can be calculated.

Interest Calculation Process in SAP

1. Define terms of payments:

T.code: OBB8
path: IMG =>fin. accting=>AP AR=>Business transactions=>outgoing invoice and credit memo=> maintain terms of payment

2. Define Interest Cal indicators / type:
T.code: OB46
path: IMG=>fin. accting=>AP AR=>Business transactions=>interest calculation global settings=>define interest cal types
Here in int cal type select ‘p’ for int cal on line items

3. Make Interest Indicator Available to Interest Run

Program:
T.Code: OB82
path: IMG =>fin. accting=> AP AR=> Business transactions=>interest calculation global settings=> prepare int. on arreas

4. Create Reference Interest Rate:
T.code: OBAC
path: IMG =>fin. accting=> AP AR=>Business transactions=> interest calculation=> interest calculation=> define reference interest rate

5. Assign interest indicators to ref. int rate 
or define time dependant terms:
T.code: OB81
path: IMG =>fin. accting=>AP AR=> Business transactions=> interest calculation=>interest calculation=>define time dependant terms
Here in sequence # always use 1 for line item interest

6. Interest calculation account assignment:
Here we will mention how and which accounts the interest program should post.

T.code: OBV1
path: IMG =>fin. accting=>AP AR=>Business transactions=> interest calculation=>interest posting =>prepare interest on arreas calculation (customers)

Also See: What is General Ledger Planning in SAP?