No-Decompression Limit (NDL)

The maximum time a diver can spend at a given depth and still ascend directly to the surface without mandatory decompression stops.

The no-decompression limit is the time you can stay at a given depth and still make a direct ascent to the surface, with no mandatory stops. Underwater, your body absorbs nitrogen from your breathing gas in proportion to depth and time. The NDL marks the point where absorbed gas is still low enough that a normal, slow ascent releases it safely. Deeper means shorter: as a reference, air NDLs run around 50 minutes at 18 m but only about 10 minutes at 40 m, with exact numbers varying by table and computer algorithm.

Your dive computer tracks NDL continuously, recalculating as you change depth, which is why a multilevel dive that gets progressively shallower earns you more time than a square profile at maximum depth. Diving nitrox extends NDLs because the gas contains less nitrogen. Repetitive dives start with residual nitrogen from earlier dives, so their limits are shorter until a surface interval clears the load.

Recreational diving is defined by staying inside the NDL. Most divers plan to turn the dive or ascend with several minutes of no-stop time remaining rather than riding the limit to zero, keeping a buffer against decompression sickness and instrument differences. Watch the NDL display throughout the dive rather than checking it only at maximum depth, since an unnoticed slide deeper along a reef can consume no-stop minutes surprisingly fast.