How to add interest up to today's date?

[John Bibby]

Can anybody advise me please on how best to do the following within Gnucash?

I want to store a % rate of interest with each account, and then get the
interest up to today's date automatically calculated and included in a
Report

e.g. if the account has balance $100 exactly a year ago, and if it is 5%
interest, then I'd like it to record
(date one year ago)              $100
(interest as at today's date) $5
Total with interest                  $105

Thanks
JOHN BIBBY