We study optimal government debt maturity in a model where investors derive monetary servicesfrom holding riskless short-term securities. In a simple setting where the government is the onlyissuer of such riskless paper, it trades off the monetary premium associated with short-term debtagainst the refinancing risk implied by the need to roll over its debt more often. We then extend themodel to allow private financial intermediaries to compete with the government in the provision ofmoney-like claims. We argue that if there are negative externalities associated with private moneycreation, the government should tilt its issuance more towards short maturities. The idea is that thegovernment may have a comparative advantage relative to the private sector in bearing refinancingrisk, and hence should aim to partially crowd out the private sector's use of short-term debt.
In this paper, we study the question of how the government should optimally determine thematurity structure of its debt. We focus on situations where there is no question about thegovernment's ability to service its obligations, so the analysis should be thought of as applying tocountries like the U.S. that are seen to be of high credit quality.1 The primary novelty of our approachis that we emphasize the monetary benefits that investors derive from holding riskless securities, suchas short-term Treasury bills. These benefits lead T-bills to embed a convenience premium, i.e., tohave a lower yield than would be expected from a traditional asset-pricing model.
We begin with the case where the government is the only entity able to create riskless moneylikesecurities. In this case, optimal debt maturity turns on a simple tradeoff. On the one hand, as thegovernment tilts its issuance to shorter maturities, it generates more in the way of monetary servicesthat are socially valuable; this is reflected in a lower expected financing cost. On the other hand, astrategy of short-term financing also exposes the government to rollover risk, given that futureinterest rates are unpredictable. As a number of previous papers have observed, such rollover riskleads to real costs insofar as it makes future taxes more volatile.
This tradeoff yields a well-defined interior optimum for government debt maturity, unliketraditional tax-smoothing models which imply that government debt should be very long term. It alsoimplies a number of comparative statics that are borne out in the data. Most notably, it predicts thatgovernment debt maturity will be positively correlated with the ratio of government debt to GDP, apattern which emerges strongly in U.S. data. The intuition is that as the aggregate debt burden grows,the costs associated with rollover risk-and hence with failing to smooth taxes-loom larger.
The simple tradeoff model also captures the way in which Treasury and Federal Reservepractitioners have traditionally framed the debt-maturity problem. According to former TreasurySecretary Lawrence Summers: