Textile microfibers are one of the most important sources within primary microplastics. These have raised environmental concerns since its recent identification as pollutants. However, there are still no accurate models to assess their contribution to the microplastic pollution. Hence, in this study, a method to estimate the mass flow of microfibers detached from household laundry that reaches aquatic environments has been developed. The method considers a set of parameters related to the detachment of microfibers, which are, basically: (1) the detachment rate of microfibers from different textile garments, (2) the volume of laundry effluents, (3) the percentage of municipal water that has been treated, (4) the type of used-water treatment applied, and, (5) the proportion of front- versus top-loading washing machines. In this way, 0.28 million tons of microfibers per year were estimated to reach aquatic environments, which is approximately half than the last published valuation. Finally, hypothetical situations were simulated to evaluate the reduction of microfibers by the modification of some of the parameters at different levels (consumer, government entities, and industry). Thus, depending on the implanted alternatives, microfibers that reach the aquatic environments could be reduced between 30% and 65%.