The nominal yield on a bond is simply the percentage of interest to be paid on the bond periodically.

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Romney has little municipal bond interest income, which means he paid more Massachusetts state taxes than others customarily do.

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Yield factors in both the interest rate paid by the bond and the actual price of the bond.

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But the case commands a great deal of attention because it would transform the country's fixed income markets if the Court determines out-of-state bond holders should get refunds for the interest they've paid on these investments.

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Interest on those bonds are paid back to the bond holders through the unlimited taxing powers of the US government, which is what makes them AAA rated.

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Bond ETFs pay out interest through a monthly dividend, while any capital gains are paid out through an annual dividend.

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In the late 1980s and early 1990s, they offered individuals annuities that paid guaranteed interest rates much higher than were available in the bond market.

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And while Tuesday's bond sale went well, at a 5.7% annual interest rate, Portugal paid dearly for it.

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Italy's government paid an interest rate of 6.47% to borrow 3bn euros for five years at a bond auction, up from 6.3% last month.

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