Skip to main content
Calcimator

Dive Profile Planner Calculator

Plan recreational dives using no-decompression limits (NDL). Calculates NDL at depth, safety stop duration, pressure group, and repetitive dive guidance.

About this calculator

No-decompression limits (NDL) define how long you can stay at a given depth before your body absorbs enough nitrogen to require staged decompression stops on ascent. This calculator looks up your planned depth against a simplified table of NDL values (loosely modeled on published recreational tables, from 219 minutes at 10 m down to 8 minutes at 42 m) and linearly interpolates between the listed depths for anything in between. It then compares your planned bottom time to that limit to compute an NDL usage percentage and a simple within/exceeds flag. For repetitive dives — a second dive within six hours of the first — the calculator applies a residual nitrogen penalty that shrinks your effective NDL, easing off as your surface interval lengthens (a full 50% penalty at zero surface interval, tapering to none by six hours).

It also derives a rough pressure group (an A-through-Z style nitrogen-loading indicator) by mapping NDL usage linearly onto a 0–25 scale, and from that estimates a minimum surface interval and a maximum safe depth for your next dive. Safety stops are recommended at 3 minutes for any dive past 10 m, extending to 5 minutes once you're past 30 m or have used 80% or more of your NDL. This is a planning approximation built for illustration, not a certified dive computer or an official dive table — always carry and follow a real dive computer or table, and never push a repetitive dive plan to the edges this tool suggests.

Inputs

m

Results

No-deco limit (min)

45

NDL usage (%)

67

Within NDL?1
Safety stop (min)3
Pressure group (0-25)17
Min surface interval (min)210
Max repetitive depth (m)22
How to Use This Calculator
  1. Enter your planned maximum depth in meters (recreational limit is 40 m).
  2. Set your planned bottom time in minutes.
  3. Indicate if this is a repetitive dive (within 6 hours of the previous dive).
  4. If repetitive, enter your surface interval in minutes to account for residual nitrogen.
  5. Read No-Deco Limit (NDL) in minutes and ensure your planned time stays below 80% of NDL for a safety margin.
  6. Note the Safety Stop duration at 5 m and the Minimum Surface Interval before your next dive.

How the result changes with Planned depth (m)

Planned depth (m)No-deco limit (min)NDL usage (%)
1021914
158535
3020150
428375

What each input means

Planned depth (m)
Maximum planned depth in metres. Recreational limit is 40 m.
Planned time (min)
Planned bottom time in minutes.
Repetitive dive?
0 = first dive of the day, 1 = repetitive dive (within 6 hours of previous).
Surface interval (min)
Time since previous dive surfaced (only applies to repetitive dives).

What each result means

No-deco limit (min)
Maximum time at this depth without requiring decompression stops.
NDL usage (%)
Percentage of the NDL consumed by your planned time. Keep below 80% for safety margin.
Within NDL?
1 = your planned time is within the no-decompression limit. 0 = exceeds NDL.
Safety stop (min)
Recommended safety stop duration at 5 metres.
Pressure group (0-25)
Nitrogen loading level after dive (0=A to 25=Z). Lower is better.
Min surface interval (min)
Minimum surface interval before next dive to reach a safe nitrogen level.
Max repetitive depth (m)
Recommended max depth for a repetitive dive after 1 hour surface interval.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Planned depth (m) = 20, Planned time (min) = 30, Repetitive dive? = 0, Surface interval (min) = 60 = 4 input(s) provided
  2. Calculate No-deco limit
    No-deco limit
    45 = 45
  3. Calculate NDL usage
    NDL usage = (plannedTimeMin / adjustedNdl) * 100
    67 = 67
  4. Calculate Within NDL?
    Within NDL?
    1 = 1
  5. Calculate Safety stop
    Safety stop
    3 = 3

Engine last updated . Checked against 3 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.

Frequently Asked Questions

Why does my no-decompression limit shrink for a repetitive dive at the same depth?

A repetitive dive starts with residual nitrogen still in your tissues from the first dive. The calculator applies a penalty that reduces your effective NDL — as much as 50% right after surfacing, tapering down to no penalty once your surface interval reaches six hours — reflecting how off-gassing over time frees up nitrogen headroom for the next dive.

How is the pressure group figure calculated, and why is it a number instead of a letter?

The calculator maps your NDL usage percentage linearly onto a 0–25 index that mirrors the classic A-through-Z pressure-group scale used on printed dive tables — 40% NDL used lands around index 10, for example. It's a simplified proxy for nitrogen loading based on time alone, not a lookup against real multi-tissue compartment data.

Why does the recommended safety stop jump from 3 to 5 minutes?

The calculator extends the stop to 5 minutes whenever your depth is 30 m or deeper, or you've used 80% or more of your NDL — both situations where you're carrying more nitrogen than a typical recreational dive and benefit from extra off-gassing before surfacing. Shallower dives that stay under those thresholds get the standard 3-minute stop instead.

How accurate is the NDL table this calculator uses?

It's a simplified table loosely modeled on published recreational dive tables, with values linearly interpolated between the listed depths — it isn't a full multi-tissue decompression algorithm like the ones running inside a dive computer. Treat its numbers as planning estimates for illustration, and always dive within the limits shown by an actual certified dive computer or table.

Related Calculators

The questions that sit next to this one — chosen by subject, including calculators filed under a different category.

Water Sports & Diving

Dive Decompression Calculator

Estimate no-decompression limits, safety stop requirements, and dive risk levels. For educational planning only — always use certified dive tables or a dive computer.

Diving

Dive Trip Cost Calculator

Estimate total dive trip costs including flights, accommodation, dive packages, gear rental, Nitrox fills, food, and insurance.

Diving

Dive Log Statistics Calculator

Analyze your diving history to estimate SAC rate, air consumption efficiency, experience level, and depth-to-experience safety ratio.

Diving

Gas Planning Calculator

Plan your gas supply using SAC rate, depth, and time. Calculates consumption at depth (Boyle's Law), maximum bottom time, turn pressure, and reserve adequacy.

More in Sports, Outdoors & Recreation.