The Kongsfjord basin in northwest Svalbard is the site of a number of interdisciplinary studies concerned with the effect of fresh water from seasonal snow and glacier melt on the physical and biological environment. We use an energy-balance model coupled with a subsurface snow model to simulate the long-term climatic mass-balance evolution of the glaciers and the seasonal snow development of nonglacierized parts of the Kongsfjord basin. Runoff from both glacierized and nonglacierized parts of the basin is simulated to quantify the fresh water flux to the fjord. The model is calibrated with long-term mass-balance data measured at four glaciers, and with automatic weather station data. The simulated area-averaged climatic mass balance for the whole basin is positive (+0.23 m w.e. a−1) over the period 1980–2016; however, the trend for net mass balance is not statistically significant over the simulation period, despite the observed ongoing summer warming. Refreezing equals 0.24 m w.e. a−1, which is equivalent to 17% of the total mass gain from precipitation and moisture deposition. Total runoff comprises contributions from seasonal snow in the nonglacierized area (16%) and glacier discharge (84%). Model time series shows a significant increasing trend for annual glacier runoff (6.83 × 106 m3 a−1) over the simulation period.