In the context of climate change and global glacier shrinkage, we have simulated the evolution of the biggest glacier in the Pyrenees (Aneto glacier) into the future using a distributed daily temperature index model. This model accounts for surface distinction and surface ageing (from fresh snow to ice) as well as for changes in surface glacier elevation over time. The slow ice velocity of the glacier allows us to neglect ice dynamics in the projections. We calibrate the model’s melt factor, which in the temperature index model translates temperatures above a given threshold into ice and snow melt. For the calibration we rely on detailed ice thickness and ice thickness change measurements at the glacier, and we force the model with climate data from ISIMIP3b (temperature and precipitation) for the 2011-2020 period. Calibration shows a non homogenous response to climate, that is, a different melt factor for different locations, the melt factor being lower in those more exposed to snow accumulation by avalanche or at lower elevations where melt might be reduced by debris cover. The low melt factor all over the surface has been found as a consequence of a warm bias in the climate forcing data, after comparing it to in situ AWS data for the same period (2011-2020). Applying 15 different future climate forcing from the Coupled Model Intercomparison Project (CMIP6) ensemble as well as different model setups, we have been able to estimate the melt of the glacier in terms of ice volume and area reduction. The melt year of every grid point is computed at a 30mx30m resolution. Glacier disappearance is projected to happen between 2037 and 2048, depending on the model set-up and forcing data. The influence of the model parameters on the melt horizon is low (<2yr). Melt is still dominated by climate, even though topographic effects also play an important role. We see no difference between the various greenhouse gas emission scenarios, which indicate that the natural variability of the climate of the next decades overlaid with current warming will decide on the fate of the Aneto. In the last phase of its evolution, the glacier will be split and confined in accumulation or shaded zones, with a lower melt rate, during its transition to an ice patch. The extrapolation to the other remaining glaciers in the mountain range is not straightforward even though we can expect similar results for the biggest glaciers (Ossue, Maladeta, Monte Perdido). We discourage the use of our temperature index mass balance model for the other remaining glaciers (15) due to their enhanced topoclimatic forcing.