The impetus of the present study was to scrutinize the impact of planning and proficiency on 172 EFL learners' written task performance regarding concept load, fluency, complexity and accuracy. Planning was operationalized at two levels: pretask planning (PTP) and online planning (OLP). Participants of this study were two groups, high and low proficiency learners who were randomly chosen. The first group was required to plan for their performance for 10 minutes and take notes before they performed the tasks, whilst the participants in the second group began writing immediately and took time as long as they like. The participants' performances were then analyzed utilizing paired samples t-test. The results of statistical analysis showed that low-proficiency learners appear to benefit more from planning time with respect to concept load, fluency, and complexity. On the other hand, high-proficiency learners were advantaged by planning time concerning concept load and accuracy.