This paper provides a recursive empirical analysis of the scope for cost minimization in public debt management when the debt manager faces a given short-term interest rate dictated by monetary policy as well as risk and market impact constraints. It simulates the ‘real-time’ interest costs of alternative portfolios for UK government debt between April 1985 and March 2000. These portfolios are constructed using forecasts of return spreads based on a recursive modelling procedure. While we find statistically significant evidence of predictability, the interest cost savings are quite small when portfolio shares are constrained to lie within historical bounds.