What is the meaning of Sinking Fund?

Sinking Fund is a requirement specified in a bond indenture that obligates the firm to annually retire a specified portion of the debt. A fund set up by a company to retire, over a period of time, the major part of a preferred share issue, or a debt issue prior to maturity. The fund helps to "pay off" the debt issue over the term of the issue and can be compared to principal payments made by a mortgage holder. Even though the issue is outstanding until maturity, the small incremental payments made under a sinking fund can make the maturity of the bond issue less onerous on the company. Instead of having to re-fund the entire issue, there may only be a small outstanding balance. A sinking fund security is attractive to investors as there is more assurance that the debt will be repaid on maturity.