The bud development period was estimated using shoot growth data from a Phytotron study in which six full‐sib familiesof Picea abiesL. (Karst.) (Norway spruce) were grown for six growth periods. Simple algebraic relationships based on assumptions of the relationship between shoot growth and bud development were used. The estimated bud development period, defined as the period when the budscale and needle primordia were initiated, decreased as growth periods advanced. Furthermore, the relationship between the period of production of free growth needles and bud scales to that of predetermined needle primordia was surprisingly constant irrespective of the change in free growth. These results indicate that free growth during one year did not encroach on the period of predetermined growth, but instead increased the amount of predetermined growth.