The aim of this study was to evaluate the balance (harmonization ratio, HR) between vegetative period (VP) and grain filling period (GFP) based on thermal times for bread wheat cultivars (Seri-82, Genc-99 and Golia), and the effect of nitrogen rates (50, 100, 150, 200 and 250 kg N ha -1) on this balance value. In the experiment, VP, GFP, days to maturity (DM), HR value and grain yield (GY) were evaluated and correlation coefficients were used to determine the relationships between these traits. HR values were significantly different for years, cultivars and nitrogen rates. Between the years, the highest HR value (0.419) and higher GY (7592.5 kg ha-1) were obtained in 2001-02 cropping year compared to 2000-01 cropping year with lower HR value (0.366) and less GY (6584 kg ha-1). Mean HR value was also calculated as 0.393 over all experiment data. However, cultivars were not significantly different for GY, while they were significantly different for HR value. However, both HR values and GY were around the mean values. All investigated traits were increased by nitrogen rates. The highest GY was obtained from 150 kg N ha-1 level with 7402 kg ha-1, at this level HR value was 0.392 and it was almost equal to mean HR value (0.393) which was calculated over all the experiment data. The lowest GY was also obtained from 50 kg N ha-1 level with 6763 kg ha-1 GY, at this level HR was also lowest (0.369). Key Words: wheat, grain filling period, vegetative period, harmonization ratio, grain yield.