What is NDL in diving?

NDL stands for no-decompression limit: the maximum time you can spend at a given depth and still ascend directly to the surface without mandatory decompression stops. Stay inside it and a slow, direct ascent is always open to you — recreational diving is built around never crossing this line.

How does depth change the NDL?

The deeper you go, the faster your body loads nitrogen and the shorter the limit. As a ballpark from recreational air tables: roughly 50–60 minutes at 18 m, but only about 20 minutes at 30 m. Treat those as approximate — computers and tables differ.

What else affects it?

• Depth and time — the two inputs every table and computer works from.
• Breathing mix — nitrox carries less nitrogen than air, so it extends the NDL at the same depth.
• Repetitive dives — residual nitrogen from earlier dives shortens the limit on the next one.

How do divers track it?

Your dive computer continuously shows the remaining NDL for your current depth. Plan the dive so you never see zero — ascending even a few metres buys minutes back.

What happens if you exceed it?

You take on a decompression obligation: mandatory stops on the way up, calculated by your computer. Skipping them risks decompression sickness, and diving that plans for deco stops requires dedicated training.

Even well inside the NDL, ascend slowly and finish with a safety stop.