We study the existence of a threshold level of inflation for the U.S. economy over 1801–2013, beyond which it has a negative effect on economic growth. A combination of nonparametric (NP) and instrumental variable semiparametric (SNP-IV) methods obtain inflation thresholds for the United States. The results suggest that the relationship between growth and inflation is hump shaped –that higher levels of inflation reduce growth more compared to low inflation or deflation. The strongest result to emerge from the study consistently shows that inflation above two per cent negatively affects growth. Two additional parametric methods confirm this finding. Another important result is that high or very low levels of inflation are undesirable and are associated with lower growth – hinting that a growth maximizing value of inflation exists.