This paper examines the expression of futurity in Spanish, specifically the periphrastic future (PF), the morphological future (MF), and the present indicative (PI) in heritage language learners (HLLs) and second language learners (L2 learners), a comparison that allowed us to explore whether linguistic experience provides HLLs an advantage over L2 learners in the domain of morphosyntax. These forms (PF, MF, and PI) are regulated by certainty, temporal distance, and the presence of temporal adverbials. Previous research showed that L2 learners acquire some of these linguistic constraints and that HLLs tend to reduce the MF to modal uses. Data from a contextualized acceptability judgment task completed by 46 HLLs and 42 L2ers manipulated for verb form, certainty, temporal distance, and adverb and revealed that (i) the PF and the MF were generally rated higher than the PI, (ii) HLLs were sensitive to the three linguistic factors examined, while the L2ers’ sensitivity was modulated by proficiency, and, relatedly, (iii) the two groups differed in the effect of proficiency. For the L2 learners, an increase in proficiency led to a closer pattern to that of monolingual native speakers (only for temporal distance). Differences in exposure to and instruction in Spanish are discussed as possible sources of these differences.