In this method, the purchase of an asset is considered an investment of capital on which a certain rate of interest is earned. The cost of the asset and the interest are written down annually by equal instalments until the book value of the asset is reduced to nil. 

The annual charge by way of depreciation is found out from the annuity tables. The annual charge for depreciation will be credited to asset account and debited to depreciation account while the interest will be debited to asset account and credited to interest account. The disadvantage of this method is that it is a complicated method to charge depreciation. Secondly, the burden on Profit and Loss account goes on increasing with the passage of time and the amount of interest goes on diminishing as years pass by. 

Thus this method is best suited to those assets which require considerable investment and don’t require frequent additions.