Regression functions are presented for estimating the thinning response of the annual‐ring‐width increment in single trees of Scots pine(Pinus sylvestrisL.) and Norway spruce(Picea abies(L.) Karst.). The thinning response of a tree is defined as the ratio between the actual annual‐ring width and the corresponding assumed annual‐ring width unaffected by thinning. Optional growth models are presented which isolate the thinning response. The models allow for a quantitative determination of the role of thinning within the complex growth process. Given knowledge of the time, intensity, and method of the thinnings, the models allow estimation of the total response to thinning. This response is influenced by all previous thinnings—active as well as natural, induced by crowding—in the stand in question.