Objectives: To evaluate in how many cancer-related Cochrane reviews hazard ratio (HR)-based absolute effects in summary of findings (SoF) tables have been correctly calculated and reported. Study Design and Setting: We identified all Cochrane cancer intervention reviews that reported an HR for at least one outcome and provided a SoF table, published between January 2011 and December 2017 in the Cochrane Database of Systematic Reviews. Results: In 28 reviews (29%) of 96 included Cochrane reviews, absolute effects in the SoF tables were calculated in a correct manner. In 23 reviews (24%), absolute effects had been correctly calculated, but there was no explanation given why authors calculated event-free survival (e.g., overall survival) throughout the review but reported number of events in SoF tables (e.g., death). Twelve reviews (13%) provided incorrect absolute effects. For seven reviews (7%), it was unclear if absolute effects were correctly calculated. In 26 (27%) reviews, no absolute effects based on the given HR were calculated. Conclusions: In less than one-third of cancer-related Cochrane reviews, absolute effect size estimates were correctly calculated and reported. There is a need for guidance on how to calculate and report absolute effect estimates based on HR data.