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The annual effective discount rate expresses the amount of interest paid/earned as a percentage of the balance at the end of the (annual) period. This is in contrast to the effective rate of interest, which expresses the amount of interest as a percentage of the balance at the ''start'' of the period. The discount rate is commonly used for U.S. Treasury bills and similar financial instruments. For example, consider a government bond that sells for $95 and pays $100 in a year's time. The discount rate is : The interest rate is calculated using 95 as the base : For every effective interest rate, there is a corresponding effective discount rate, given by : or inversely, : Given the above equation relating to it follows that : where is the discount factor or equivalently, : Since ,it can readily be shown that : This relationship has an interesting verbal interpretation. A person can either borrow 1 and repay 1 + ''i'' at the end of the period or borrow 1 - ''d'' and repay 1 at the end of the period. The expression ''i'' - ''d'' is the difference in the amount of interest paid. This difference arises because the principal borrowed differs by ''d''. Interest on amount ''d'' for one period at rate ''i'' is ''id''. ==Annual discount rate convertible thly== A discount rate applied times over equal subintervals of a year is found from the annual effective rate d as : where is called the annual nominal rate of discount convertible thly. : is the force of interest. The rate is always bigger than d because the rate of discount convertible pthly is applied in each subinterval to a smaller (already discounted) sum of money. As such, in order to achieve the same total amount of discounting the rate has to be slightly more than 1/pth of the annual rate of discount. 抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)』 ■ウィキペディアで「annual effective discount rate」の詳細全文を読む スポンサード リンク
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