The natural rate of interest—the real interest rate consistent with output equaling its natural rate and stable inflation—plays a central role in macroeconomic theory and monetary policy. Estimation of the natural rate of interest, however, has received little attention. We apply the Kalman filter to estimate jointly time-varying natural rates of interest and output and trend growth. We find a close link between the natural rate of interest and the trend growth rate, as predicted by theory. Estimates of the natural rate of interest, however, are very imprecise and subject to considerable real-time measurement error.

Several specifications of state-space models are used to obtain estimates of the NAIRU for the G7 except Japan, plus Australia, over the past 28 years. A Phillips curve-type regression is shown to deliver estimates that do not mimic low-frequency movements in unemployment rates, even when a drift is included in the specification of the NAIRU. Standard errors around the estimates are extremely large. Using information about the behavior of unemployment, in addition to inflation, alleviates both these shortcomings.