Math and reading are fundamental skills for academic success and have an influence on students’ future job satisfaction and overall SES (Ritchie and Dates, 2013). A high volume of research has been dedicated to investigating the cognitive and neural underpinnings of both reading and math in isolation, with much less attention being directed to understanding the relationship between them. The available evidence about the nature of this relationship consistently points toward an association between arithmetic and phonological skills. This association seems specific to arithmetic facts that are typically solved using retrieval strategies (i.e., multiplication or small addition problems) and persists even after controlling for the effect of domain-general factors (De Smedt, Taylor, Archibald and Ansari, 2010). At the neural level, multiple neuroimaging studies have reported that some of the brain regions that are typically associated with phonological processing (i.e., inferior temporal gyrus, middle temporal gyrus, etc.) are also recruited during arithmetic fact retrieval (Arsalidou and Taylor, 2011; Dehaene et al., 2003; Evans et al., 2014; Prado et al., 2014). Moreover, one recent meta-analysis has identified clusters of brain activation that seem to be shared between arithmetic and phonology (Pollack and Ashby, 2018). By summarizing the results of more than 70 fMRI studies, Pollack and Ashby provide robust evidence to suggest shared neural pathways for arithmetic and phonology. However, this metanalysis shares one important limitation with most of the earlier research: the data available for the study of the relationship between phonology or arithmetic comes from paradigms including only one of those processes, and not both. In order to unravel the real nature of this relationship we need more direct evidence that compares the neural activity associated with arithmetic and phonology within the same participants. To our knowledge, only one other study by Andin, Fransson, Rönnberg and Rudner (2015) has directly compared the neural activity associated with phonological decoding and arithmetic processing, within the same participants. They found significant brain activation for both tasks along predefined areas such as the left inferior frontal gyrus. However, the specific mechanisms that drive the activation across those shared regions are still unclear. Even within the same participant, overlapping brain regions is a condition necessary, but not sufficient to confirm that phonological decoding and arithmetic tap into the same neural mechanisms. Both tasks may be recruiting networks that intersect but are still independent, which would result in a similar set of regions showing activation above baseline for both tasks, even though the underlying processes are completely different. In the present study, we aim to contribute to the understanding of possible shared neural mechanisms between arithmetic and phonological decoding by comparing the multivariate patterns of neural activity obtained during a rhyming (tapping into phonological processing) and two arithmetic tasks (small addition problems and large addition problems) within the same participants. We will use Representational Similarity Analysis to assess whether those regions that are significantly active during both arithmetic and phonological decoding, also display similar patterns of activation across multiple voxels. Moreover, we will determine whether the similarity in the patterns of activation is driven by the recruitment of phonological processes during problems that are typically solved using a retrieval strategy (i.e., small problems), compared to those that are more likely to require actual numerical computations (i.e., large problems). Finally, we will run similar analyses across one sample of adult participants and another sample of children. This will allow us to compare potential differences in the way phonology and arithmetic relate to one another in two distinct developmental moments.