A serial bond is a bond issuance where a portion of the total number of bonds are paid off each year. This results in a gradual decline in the total amount of the issuer's debt outstanding. For example, a $1,000,000, ten-year serial bond will have $100,000 of bonds mature once a year for ten years.
A serial bond is designed to support the financing needs of a capital project that delivers a steady stream of funds to pay down the debt over time. For example, a toll road may require initial funding with a bond issuance, after which toll proceeds are used to pay off the bonds over a long period of time. The same situation arises for an apartment complex, where bonds are used to pay for construction of the complex, and the resulting rents are used to pay for the bonds.
Conversely, serial bonds are not suitable when the cash flows expected to be generated by a project funded with the bonds will be irregular, delayed, or uncertain. In such cases, structuring a bond as a serial bond could result in a default rather early in the buy-back period.
The advantage to the issuer of a serial bond is that less interest will be paid over the life of the bonds, since the aggregate amount of cash loaned to the issuer is greatly reduced. The advantage to the investor is the reduced risk of default, since the issuer's repayment liability is constantly declining.