You'll know how much interest you'll receive from the beginning, but you can also profit from price moves on the secondary market. Thinkstock By the editors of Kiplinger's Personal Finance Updated January 2015 Bonds can help diversify your portfolio, but they are not risk-free. Find out how bonds work and how to put them to work for you.See Also: The Basics of Investing in Bonds When a new bond is issued, the interest rate it pays is called the coupon rate, which is the fixed annual payment expressed as a percentage of the face value. For example, a 5% coupon bond pays $50 a year interest on each $1,000 of face value, a 6% coupon bond pays $60 and so forth. That's what the issuer will pay — no more, no less — for the life of the bond. But it may or may not be the yield you can earn from that issue, and understanding why is the key to unlocking the real potential of bonds. Take a new bond with a coupon interest rate of 6%, meaning it pays $60 a year for every $1,000 of face value. What happens if interest rates rise to 7% after the bond is issued? New bonds will have to pay a 7% coupon rate or no one will buy them. By the same token, you could sell your 6% bond only if you offered it at a price that produced a 7% yield for the buyer. So the price at which you could sell would be whatever $60 represents 7% of, which is $857.14. Thus, you'd lose $142.86 if you sell. Even if you don't sell, you suffer a paper loss because your bond is now worth $142.86 less than you paid for it. It is selling at a discount. Advertisement But what if interest rates were to decline? Say rates drop to 5% while you're holding your 6% bond. New bonds would be paying only 5% and you could sell your old bond for whatever $60 represents 5% of. Because $60 is 5% of $1,200, selling your 6% bond when interest rates are at 5% would produce a $200 capital gain. That $200 is called a premium. Actual prices are also affected by the length of time left before the bond matures and by the likelihood that the issue will be called. But the underlying principle is the same, and it is the single most important thing to remember about the relationship between the market value of the bonds you hold and changes in current interest rates: As interest rates rise, bond prices fall; as interest rates fall, bond prices rise. The further away the bond's maturity or call date, the more volatile its price tends to be. Varieties of Yield Because of this relationship, the actual yield to an investor depends in large part on where interest rates stand the day the bond is purchased, so the vocabulary of the bond market needs more than one definition for yield. Coupon yield, as described above, is the annual payment expressed as a percentage of the bond's face value. Current yield is the annual interest payment calculated as a percentage of the bond's current market price. A 5% coupon bond selling for $900 has a current yield of 5.6%, which is figured by taking the $50 in annual interest, dividing it by the $900 market price and multiplying the result by 100. Advertisement Yield to maturity includes the current yield and the capital gain or loss you can expect if you hold the bond to maturity. If you pay $900 for a 5% coupon bond with a face value of $1,000 maturing five years from the date of purchase, you will earn not only $50 a year in interest but also another $100 when the bond's issuer pays off the principal. By the same token, if you buy that bond for $1,100, representing a $100 premium, you will lose $100 at maturity. The yield to maturity can dramatically affect investment results.