What is the residual nitrogen penalty (RNT)?

After a dive, nitrogen stays dissolved in your body. On a repetitive dive, that leftover nitrogen 'eats into' your bottom time at the new depth. The penalty (also called Residual Nitrogen Time, RNT) is the number of minutes, at your next dive's depth, that represent the nitrogen still in your body from the previous dive. The planner adds it to your planned bottom time to check the pressure group and remaining NDL.

How many dives can I plan?

As many as your day holds, up to six here. Add a dive and the planner chains it: it carries your pressure group and oxygen exposure from one dive to the next, applies each surface interval, and recomputes the bottom time you really have left. The classic two-dive check is just the first two rows of the same plan.

How much bottom time do I really have on my next dive?

At any depth there is a no-decompression limit (NDL): the maximum bottom time before a mandatory decompression stop. On a repetitive dive you subtract your residual penalty from that NDL: the result is the bottom time you actually have available. The planner shows both the NDL at your depth and the time left after your residual penalty, for every dive.

What is a pressure group?

A pressure group (or repetitive group) is a letter from A to Z that represents how much residual nitrogen remains in your body after a dive. 'A' is the least nitrogen loading and 'Z' the most. You end a dive in a group, the surface interval drops you to a lower group, and that is the group you start the next dive with before you reach a new end group.

What does the decompression guidance use?

When a dive exceeds its no-decompression limit, the planner reads the decompression time straight from the dive table row that matches your depth and bottom time. It never invents tissue-model numbers: it shows the table's required minutes and a conservative 3 m stop, and tells you to ascend no faster than 9 m/min. As a recreational diver, reduce the depth or bottom time instead of planning a decompression dive.

What do altitude and fresh water change?

At altitude the surface pressure is lower, so the same depth produces less pressure and less nitrogen loading. Fresh water is less dense than sea water, so pressure also builds more slowly. The planner corrects the pressure model for both, which matters for mountain lakes and quarries.

Can I share my plan with my buddy?

Yes. Press Share plan and copy the link. Anyone who opens it sees the planner with your exact dives, surface intervals and conditions already filled in, ready to review or adjust.

Total time or bottom time: which one should I enter?

Enter the total dive time, exactly as your dive computer shows it: it includes descent, time at depth, ascent and safety stop. The planner estimates the bottom time at your max depth by removing the ascent to 6 m (at 9 m/min, rounded up), a 3-minute safety stop and the final 2-minute ascent to the surface. For example, a 50-minute dive to 18 m becomes a 43-minute bottom time.

Can I use Nitrox for repetitive dives?

Yes, and it helps. Nitrox reduces the nitrogen fraction in your breathing gas, which lowers your Equivalent Air Depth (EAD). A lower EAD means less nitrogen absorbed, so you end the dive in a lower pressure group, carry less residual nitrogen into the next dive, and keep more bottom time. Select your mix to see how your penalty and remaining time change.

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Repetitive Dive & Surface Interval Planner

Plan your dives and know exactly how much bottom time you really have on each one: residual nitrogen penalty (RNT), pressure groups, remaining NDL, cumulative oxygen exposure and safety stops, all in one timeline. Add two dives or a full liveaboard day, and see the whole plan update as you type.

What is a surface interval?

The surface interval is the time you spend out of the water between two dives. During it, your body releases some of the nitrogen absorbed on the first dive, so your pressure group drops and the next dive starts with less residual nitrogen. The longer the interval, the lower the residual nitrogen penalty (RNT) and the more bottom time you really have on the next dive.

Planning multiple dives? Track them all with Depthlog

This tool plans your day. Depthlog tracks every dive you actually make, including surface intervals and nitrogen loading, so you never lose the picture. Free account, no credit card required.

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This tool is intended to be used as an informational and educational tool

Always check the safety regulations and follow the standards relating to repetitive diving. Consult a certified diving instructor for proper training. Read the dive safety disclaimer and the Terms of Service.

How to plan a repetitive dive

Log the first dive. Enter depth, bottom time and gas mix.
Set the surface interval. The planner lowers your pressure group from the end group of the first dive.
Read the next dive limits. Enter the next depth and gas mix to see the residual nitrogen penalty (RNT) and the bottom time you really have.

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