The mass balance year runs from autumn to autumn, when ice masses are at their smallest volume.

Generally, glaciers increase in size during the winter, this is a positive regime in the glacial budget. A positive regime causes the glacier to grow and advance at the front.

In summer there is more ablation than accumulation due to rising temperatures. This means that there is a negative regime in the glacial budget. A negative regime causes the glacier to shrink and retreat at the front.

If accumulation in winter is balanced by ablation in the summer, the annual net balance for the glacier is zero.

Trends in the annual net balance of glaciers is usually calculated on a ten-year basis.

The main techniques in measuring glacier net balance are:
- Altimitry - measures the time taken by a radar pulse to travel from the satellite antenna to the surface and back to the satellite receiver, this measures the height of the glacier
- Gravimetry - measurement of the strength of a gravitational field
- Mass budget method - compares the amount of snow accumulation on the ice sheet and the amount of meltwater/calving leaving the glacier

Glacier Formation and Movement