Background: The usage of smartphones plays a significant role in everyday life, and smartphone addiction is significantly associated with musculoskeletal complications due to prolonged use with the maintenance of neck flexion posture. Purpose: To quantitatively assess the changes in the neck flexion angle of smartphone users in relation to the duration of usage. Method: Thirty female participants from Physical Therapy department at Umm AlQura University with ages ranged from 18 to 24 years were recruited. The participants were randomly assigned (1:1) to one of two groups, one of which performed browsing and texting tasks while standing and the other while sitting against a scaled board for 25 minutes. The experiment required only one session to observe the participants neck flexion angle variations and a photo was taken every 5 minutes from the beginning to the end of the session. Results: Neck flexion angle was significantly affected by the posture and different duration of usage, and the comparison of neck flexion angle in sitting and standing position revealed a significant difference in all durations except 10-25 minutes in the standing group. Study results suggest that sitting, which is the most frequently used position, may be a main contributing factor to the occurrence of musculoskeletal symptoms among heavy smartphone users. Conclusion: The findings revealed statistically significant effects of both posture and usage duration on neck flexion angle. Also, neck flexion angle increased significantly over time in all postures.