The return a bond provides to an investor is measured by its yield, which is quoted as a percentage.
Current yield is a commonly quoted yield calculation, used to evaluate the return on a bond for a oneyear period. It only accounts for the interest, or coupon payments, that the bond returns to investors. This yield is calculated as the bond's coupon rate divided by its current market price, but it does nothing to account for any capital gains or losses when the bond is sold. If the bond is not sold within the year, this yield calculation will provide the bondholder with an accurate assessment of his or her return. The only way a bond's current yield could be negative, using this basic evaluation, is if the investor were receiving negative interest payments, or if the bond somehow had a market value below $0  both of which are very unlikely to occur.
Other yield calculations will take into account different factors and can be used to better evaluate the returns an investor may receive, given different events.
As its name suggests, the yield to maturity (YTM) calculates the return (expressed as an annual percentage) on a bond if the investor were to hold the bond until maturity. This formula takes into account all of the coupon payments and the face  or par  value on the bond (assuming no principal defaults), and it can be seen as a more complete evaluation than current yield. However, calculating a bond's YTM is complex and involves trial and error. It is usually done by using a programmable business calculator, but you can also get an approximate YTM by using a bond yield table.
Let's consider an example: say an investor pays $800 for a bond that has has exactly two years to maturity, a face value of $1,000 and interest payments of $8 per year. Using a bond table, we could determine that the bond will have a YTM of about 10.86%. If the bond holder paid $1,200 for the bond, the YTM would be about 9.41% (It is worth noting, however, that a bond will not necessarily have a negative actual yield just because the investor paid more than face value for it.) When using the YTM calculation, it is possible to have a negative yield on a bond  it depends largely on how much you initially pay for the bond and the time to maturity.
Yields can be calculated using different formulas  there are many more than the two mentioned here  and depending on the formula used, you can end up with drastically different yields. To learn more, see our Bond Basics Tutorial, Advanced Bond Concepts and The Basics Of The Bond Ladder.
RELATED FAQS

I want to invest my emergency fund to earn interest. What is a relatively safe and ...
When considering where to put your emergency money, a key consideration is making sure you'll be able to access the money ... 
How does the money from the interest on my bond get to me?
When you buy a regular coupon bond, you are entitled to a coupon, which is typically paid at regular intervals, and the face ... 
The security which offers the best protection against purchasing power risk or inflation ...
a. fixed annuityb. common stockc. treasury bondd. certificate of deposit Answers: bDebt securities and investments that promise ... 
How are bonds rated?
Moody's, Standard and Poor's, Fitch Rating and Dominion Bond Rating Service are some of the internationally wellknown bond ...

Impact investing

Promotional CD rate (Bonus CD rate)
A limitedtime offer of a higher rate of return on a certificate ... 
Direct Bidder
An entity that purchases Treasury securities at auction for a ... 
Indirect Bidder
An entity that purchases Treasury securities at auction through ... 
Bid Wanted
An announcement by an investor who holds a security that he or ... 
Super Sinker
A bond with longterm coupons but a potentially short maturity. ...