Abstract Grant proposal summaries are a high-stakes academic genre requiring significant marketing efforts to enhance accessibility for a diverse audience. However, research in this field remains scarce. This study addresses this gap by examining the readability and jargon use in lay summaries of Collaborative Research Fund (CRF) grant proposals administered by the University Grants Committee (UGC) in Hong Kong from 2006 to 2024. The findings reveal that, despite temporal fluctuations, these summaries generally align with senior-college to college-graduate reading levels. They also contain a high average jargon density of 8.0% per text, surpassing the recommended threshold for general readership. Notably, readability measures related to structural complexity show a significant upward trend, while lexical difficulty remains stable. Meanwhile, normed jargon use presents a non-significant but visually noticeable upward trend over time. These temporal patterns suggest that these lay summaries have become more challenging to read, mostly due to individually-varied but densely embedded specialised terms in longer and more complex sentences. The findings raise concerns about the accessibility of lay summaries for non-specialists, such as interdisciplinary researchers, science communicators, policymakers, and the general public. The study concludes with a discussion and suggestions on readability and jargon use in grant proposal summaries.