No-Decompression Limit (NDL) — What It Is and Why It Matters
The no-decompression limit (NDL) is the maximum amount of time you can spend at a given depth without being required to make mandatory decompression stops during your ascent. As long as you ascend before exceeding the NDL, you can return directly to the surface (at a safe ascent rate) with only the standard safety stop at 5 meters.
NDL decreases as depth increases — at 18 meters you might have 50+ minutes of NDL, while at 40 meters it could be as short as 8 to 10 minutes. Your dive computer continuously recalculates NDL based on your actual depth profile, which is why multi-level diving on a computer typically gives you more bottom time than flat-depth table planning.
Frequently Asked Questions
What happens if I exceed my NDL?
Your dive computer will switch to decompression mode and display mandatory stop depths and times that you must complete during your ascent. Skipping mandatory deco stops significantly increases your risk of decompression sickness. If you accidentally exceed NDL, follow your computer's deco stop instructions exactly.
Does NDL reset between dives?
Partially. During your surface interval, your body off-gases nitrogen, which restores some NDL. However, residual nitrogen from previous dives means your NDL on repetitive dives will be shorter than your first dive of the day. Your dive computer tracks this automatically.
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