Free radicals critically impact and can be deleterious for biological systems. They are highly reactive and lead to unspecific damage of proteins, DNA, and lipids, causing various diseases and aging. Radical formation is followed by a plethora of subsequent reactions, most importantly radical propagation through hydrogen atom transfer (HAT). Radical formation and propagation are not only at play in biomolecules but very analogously occur in synthetic polymers, and similarly lead to damage and material aging. Due to the high reactivity of radicals, intermediate products of radical reactions can be very short-lived and therefore hard to capture experimentally. Predicting the fate of radicals in proteins or other (bio)polymers is thus of utmost relevance to better understand and combat radical-induced damage.