Much research has investigated the role of planning time in second language writing; however, the results show that there are inconsistent findings about the effects of planning time conditions on the complexity of the EFL learners' textual output. The current study attempted to consider the differential effects of planning time conditions in terms of the pre-task planning condition, the online planning condition, and the no planning condition on the complexity of writings composed by means of an argumentative task from 90 EFL learners. The results reveal that the pre-task planning condition had a marked effect on syntactic complexity and syntactic variety, but the online planning condition only benefited syntactic complexity. Rather unexpectedly, the three planning time conditions showed practically similar performance in lexical variety. The results indicate that pre-task and online planning had remarkable effects on the production of language that was more complex and syntactically varied, however, these two types of planning did not benefit lexical variety. In addition, through a consideration of Yuan and Ellis (2003) and Ellis and Yuan (2004), regarding the effects of planning on oral and written narratives, the researcher compared the results of the study to those previous and, finally, provided pedagogical implications on language practitioners and testers.