Extensive farming systems require beef cows to cope with varying environmental conditions while repeatedly producing calves. Cows use body energy reserves as a buffer in times of feed shortage and replenish reserves under a feed surplus. The aims of the research were to (1) quantify live weight (LW) and body condition score (BCS) fluctuations among farms, years and over the production cycle (mating, weaning and calving) and to (2) quantify the relationship between LW and BCS at mating, weaning and calving, for cows of different hip heights. A total of 7,649 individual cow records from nine commercial New Zealand farms with information on LW and BCS (1–10 scale, 1 = emaciated and 10 = obese) were analysed. Analyses revealed significant (P < 0.001) within-year variation in mean LW (32.4–77.2 kg) and BCS (0.4–1.8 scores) profiles among farms, but profiles were not consistent from year to year. There was a quadratic relationship (P < 0.001) between LW and BCS, such that one unit change in BCS corresponded to 15.1 kg LW increase at BCS 4–5 compared to 41.1 kg LW increase at BCS 8–9 at mating. This relationship was similar, irrespective of hip height.