The romance future and conditional tenses are the result of the grammaticalization of Latin periphrasis, mainly cantāre habeō. In some medieval Romance languages, including Catalan, two types of forms existed: synthetic forms (faré ‘I will do’) and analytical forms (fer-lo he ‘I will do it’). Analytical forms do not present univerbation and are thus less grammaticalized than synthetic forms. The present work aims to study the distribution of synthetic and analytical forms diachronically. A diachronic corpus (11th c.–16th c.) was compiled to serve this purpose. According to the syntactic restrictions of clitic placement, analytical forms could appear in the same syntactic environments than synthetic forms with postverbal pronouns (faré-lo ‘I will do it’). Therefore, only those contexts are analysed to assess the degree of grammaticalization. Some recent works point out that the grammaticalization of future and conditional was more advanced in the eastern languages of the Iberian Peninsula, such as Catalan, than in the western ones. The results from our corpus confirm these differences. In addition, the data show another grammaticalization process: the evolution of clitic placement towards a fixed preverbal position.