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The Yield to maturity (YTM), book yield or redemption yield of a bond or other fixed-interest security, such as gilts, is the internal rate of return (IRR, overall interest rate) earned by an investor who buys the bond today at the market price, assuming that the bond will be held until maturity, and that all coupon and principal payments will be made on schedule.〔(Definition of 'Yield To Maturity (YTM)' )〕 Yield to maturity is the discount rate at which the sum of all future cash flows from the bond (coupons and principal) is equal to the price of the bond. The YTM is often given in terms of Annual Percentage Rate (A.P.R.), but more usually market convention is followed. In a number of major markets (such as gilts) the convention is to quote annualised yields with semi-annual compounding (see compound interest); thus, for example, an annual effective yield of 10.25% would be quoted as 10.00%, because 1.05 × 1.05 = 1.1025.〔(Formulae for Calculating Gilt Prices from Yields )〕 ==Main assumptions== The main underlying assumptions used concerning the traditional yield measures are: * The bond will be held to maturity. * All coupon and principal payments will be made on schedule. * All the coupons are reinvested at an interest rate equal to the yield-to-maturity.〔Fabozzi, Frank. ''The Handbook of Fixed Income Securities''. McGraw-Hill, 2005, p. 87.〕 However, the paper ''Yield-to-Maturity and the Reinvestment of Coupon Payments'' says making this assumption is a common mistake in financial literature and coupon reinvestment is not required for YTM formula to hold. * The reason for the confusion is this: The YTM is equivalent to a price in the market place. You can bid a 5% YTM on a bond. In that case each cash flow will be discounted at that rate to give you a current number price for a bond. However if you take that price for the bond and annualize it at the YTM you will not get the same economic return as you would get from buying and holding the bond. For example, the paper cited above discounts the cash flows of a 5 year 5% coupon bond at a YTM rate of 5% and shows that the current price is par. However, if you buy a 5 year 5% coupon bond for $100 you would gross $125 at maturity. However if you invest $100 at a rate of 5% for 5 years you would gross: 100 * 1.05^5 = $127.63. The difference between $127.63 and $125 is the reinvestment of the coupon payments at 5%. Therefore if you want to compound the dollar amount used to purchase a bond by the YTM, you will have to reinvest the coupons at the YTM rate as well. * The yield is usually quoted without making any allowance for tax paid by the investor on the return, and is then known as "gross redemption yield". It also does not make any allowance for the dealing costs incurred by the purchaser (or seller). 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「yield to maturity」の詳細全文を読む スポンサード リンク
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