Receiving Interest

Go to display -> Statement of Accounts -> Interest Calculation -> Interest Payable/Interest receivable. Press F2 and give the date there.
Then receive interest through Accounting Voucher.

Interest Calculation

Create a ledger named 'Investment'.
Then press F11 and then press F1, set "Activate interest calculation" and "use advanced parameter" as 'yes'.
Then Alter the ledger Investment created and set the 'interest calculation option' as 'yes'. There you give the all the information required i.e. the rate of interest, time period, rounding(rounding off the decimal value), etc.