what is a amortization expense and when do we debit it and when do we credit it? Solution Amortisation expense means decline in value of goodwill, patents and other intangible assets.Allocation to expenses of cost of intangible assets. We debit while recognising amortisation expenses and the entry would be Amortization expense Dr $xxx To Accumulated amortization - Intangible Asset We credit it Deferred Income Dr XXX To Deferred amortization Income XXX.