Import tariffs are typically defined at a very detailed level, which is then used in trade negotiations. The WTO Framework Agreement of July 2004 proposes the use of a “tiered” formula where tariff lines classified in higher ‘bands’ are subject to proportionally higher cuts. Exceptions to the general rule, like sensitive products, are also defined at the tariff line level. Despite the relevance of tariff structure on trade liberalization, computable partial or general equilibrium models usually represent more aggregated products. In this respect, the literature suggests that market models can be combined with detailed tariff modules. We propose a new methodology to more accurately aggregate tariffs from the tariff line level to the one required by computable equilibrium models. The Tariff Reduction Impact Model for Agriculture (TRIMAG) uses the highest possible level of disaggregation (8 digits) and allows implementing tariff cuts and deriving the domestic price drops foreseen by alternative trade policy scenarios. Aggregated tariffs are derived by considering the substitutability effects in consumption between the tariff lines corresponding to the same aggregate product. We incorporate the tariff aggregates of TRIMAG resulting from a WTO agreement into the Common Agricultural Policy Regionalized Impact (CAPRI) partial equilibrium model. Differences between the standard tariff aggregation of CAPRI and the newly implemented methodology are illustrated. Results show that, when tariff cuts are applied at the 8 digit level, whether the substitution in consumption between tariff lines will result in a lower or higher aggregate tariff cut than the one that should directly be applied to the aggregate product is an empirical question. The selection of a limited number of sensitive tariff lines, if their share in the consumption bundle is high, might significantly raise the tariff for the corresponding aggregated product.