<title>Abstract</title> Studies that quantify the contribution of genetic improvement to crop yields typically rely on comparisons of old cultivars grown side-by-side with more recent ones. This approach, however, does not allow to distinguish gains in yield potential <italic>versus</italic> maintenance breeding that aims to keep cultivars adapted to the evolving biophysical environment, including pests, diseases, and climate change. Our analysis of long-term wheat trials from Argentina, Europe, and United States revealed an overall genetic yield improvement of 97 kg ha^{− 1} y^{− 1} (1.14% per annum) based on comparison of modern cultivars against older ‘check’ cultivars. However, nearly half of the genetic improvement (46 kg ha^{− 1} y^{− 1}) was attributable to maintenance breeding and the other half (51 kg ha^{− 1} y^{− 1}) to the higher yield potential of modern cultivars. We conclude that comparison of new <italic>versus</italic> old cultivars under current conditions leads to an overestimation of genetic gains in yield potential. <bold>One sentence summary</bold>: Crop yield potential gains are lower than reported.