This study estimates the real natural rate of interest for Korea and the United States by incorporating post-COVID-19 macroeconomic changes, and evaluates the stance of monetary policy based on these estimates. To this end, we employ a semi-structural state-space model that incorporates time-varying volatility and pandemic-related supply shocks. The results show that the real natural rate has exhibited a long-run declining trend in both countries, while output gaps have experienced substantial negative adjustments during major shock episodes. In addition, policy rates in the post-pandemic period have been maintained above the long-run nominal natural rate, suggesting that monetary policy has been conducted in a restrictive stance. By accounting for the unprecedented macroeconomic fluctuations following the pandemic, this study provides a more consistent quantitative benchmark for assessing the stance of monetary policy.