The building up over a period of a fund to replace a productive asset at the end of its useful life, or to repay a loan. In the case of a loan, the amount required for amortization depends on the interest rate that can be earned on the accumulated fund. In the case of replacement of physical assets, the amount needed depends not only on the interest rate, but also on the expected lifetime of the asset and on the rate of inflation, which affects the expected cost of replacement.