Scuba Decompression Planner
A quick way to visualize a safer ascent
This calculator is best understood as a simple safety-stop estimator, not as a full decompression engine. If you know the deepest point of a dive and the total bottom time, it gives you a rough suggestion for how long to pause at 5 m before surfacing. That makes it useful for teaching, for pre-dive what-if checks, and for seeing how a deeper or longer profile tends to push a stop recommendation upward. It is deliberately lightweight, so you can compare scenarios in a few seconds rather than digging through a larger planning workflow.
That simplicity is also the page's biggest limit. Real decompression planning depends on much more than two numbers. Dive computers and formal tables account for tissue loading, repetitive dives, ascent rate, gas mix, altitude, workload, temperature, and many other factors. So the result here should be treated as a conservative educational guide for a single-profile recreational dive, not as permission to ignore your training or equipment. If your dive plan is complex, close to limits, or operationally important, the right reference is still your dive computer, your agency guidance, and local procedures.
Within that scope, the page answers a very practical question: If I go this deep for this long, what kind of safety stop should I be thinking about at the end of the ascent? The form keeps the inputs simple, the result is shown in plain language, and the details panel restates the numbers so you can copy them into a dive log or compare several scenarios side by side.
What the two inputs mean in plain language
Max Depth (m) is the deepest point reached on the dive, entered in metres. Use the actual planned or observed depth, not a rough depth category such as “about thirty-ish.” Because the formula scales directly with depth, even a few metres of difference can change the estimate. If your source data is in feet, convert it first rather than typing the number as-is.
Bottom Time (min) is the total time spent on the dive profile that you want this simple model to represent, entered in minutes. For this calculator, the cleanest way to think about bottom time is “the time associated with the main exposure of the dive,” not the final safety stop itself. If you are sketching a planned square-profile dive, use the planned bottom time. If you are reviewing a completed dive, use the relevant time from your computer or log in minutes.
Because this estimator compresses the dive into only depth and time, it works best when the profile is already simple. A dive with several levels, a long drift, multiple gas switches, repetitive exposures, or unusual environmental stress is exactly where a more complete tool matters. In other words, the calculator is not confused by extra real-world detail because it ignores that detail entirely. That is why careful input interpretation matters: clear inputs produce a useful teaching estimate, while vague inputs can create false confidence.
How the planner turns depth and time into a stop estimate
The JavaScript on this page calculates a raw stop value by multiplying two ratios: depth divided by 10, and time divided by 60. It then applies a floor of 3 minutes and a cap of 15 minutes. The visible result is the uncapped value after those limits are applied, and the details table also gives you a rounded planning value.
Here d is maximum depth in metres and t is bottom time in minutes. The 3-minute minimum mirrors the common idea of a baseline recreational safety stop. The 15-minute cap keeps the result inside a simple teaching range rather than pretending to generate a full staged decompression schedule. If the raw formula produces 1.8 minutes, the calculator still suggests 3 minutes. If it produces 18 minutes, the display is limited to 15 minutes. That design makes the tool readable, but it also tells you something important: once a dive starts pushing toward more demanding exposure, a capped estimate is a sign to consult a proper dive-planning source instead of stretching this page beyond its purpose.
One benefit of seeing the formula laid out this clearly is that you can predict direction before you even press the button. Increase depth while holding time constant, and the stop tends to rise. Increase time while holding depth constant, and the stop tends to rise. Short, shallow dives often fall to the 3-minute minimum. Deeper or longer profiles begin to climb above it. That makes the result easy to sanity-check: if the number moves the wrong way after you edit an input, the first thing to inspect is the units you entered.
Worked example: reading the result like a diver, not a spreadsheet
Suppose you want to review a dive to 30 m with a bottom time of 80 minutes. The raw formula is:
(30 ÷ 10) × (80 ÷ 60) = 3 × 1.333... = 4.0
Because 4.0 is above the 3-minute minimum and below the 15-minute cap, the calculator returns a suggested stop of 4.0 minutes at 5 m. In the details table, you will also see a rounded planning value of 4 minutes at 5 m.
That does not mean every 30 m / 80 min dive is adequately handled by a single 4-minute pause. What it means is narrower and more useful: in this simple model, a profile of that depth and duration falls above the baseline 3-minute stop, so the page shows a longer pause. If you change only one input, the effect becomes clearer. Keep the 80-minute time but reduce the depth to 18 m, and the raw value falls to 2.4, which the calculator lifts to the 3-minute minimum. Keep the 30 m depth but extend the time much farther, and the stop climbs again. That is the real teaching value of the worked example: you can see how depth and time reinforce each other.
A good result review has three quick questions behind it. First, do the units match what you intended to enter? Second, is the magnitude believable for a simple 5 m stop estimate? Third, if you run a slightly shallower or slightly longer scenario, does the result change in the direction you would expect? When those checks all pass, the number is doing its job as a planning prompt.
Scenario comparison
The table below uses realistic sample profiles so you can see how the estimate changes as the dive grows more demanding. It is not a substitute for dive tables; it is simply a clean way to see the calculator's behavior.
| Scenario | Max Depth | Bottom Time | Raw Formula Result | Displayed Suggestion | Interpretation |
|---|---|---|---|---|---|
| Shorter recreational profile | 18 m | 35 min | 1.05 min | 3.0 min at 5 m | The raw value is low, so the minimum safety stop governs the result. |
| Longer moderate profile | 30 m | 80 min | 4.0 min | 4.0 min at 5 m | Depth and time are both high enough that the stop rises above the minimum. |
| Very demanding simple profile | 40 m | 120 min | 8.0 min | 8.0 min at 5 m | This already signals a dive that deserves proper planning beyond this lightweight estimator. |
Looking at examples like these is helpful because many people do not need a formula explained in abstract terms; they need to see how a realistic change in the dive profile shifts the recommendation. Deeper and longer profiles do not just feel more serious in a general sense. In the model used here, they mathematically increase the stop target.
How to interpret the result without over-trusting it
When you click Calculate Stops, the main result line gives you the suggested stop duration and the depth of that stop. The details panel underneath then restates the maximum depth entered, the bottom time entered, the built-in minimum stop, and the rounded stop you could plan around. That summary is useful because it lets you confirm not only the answer but also the assumptions that produced it.
Think of the result as a conversation starter with your dive plan, not as the final authority. If the page suggests the baseline 3-minute stop, that means your inputs did not push the simple formula above the minimum. If it suggests something longer, that means the dive profile is trending away from the baseline and deserves more caution. In both cases, the ascent itself still matters. A perfectly chosen stop duration does not rescue a rushed ascent, poor buoyancy control, or a profile that your computer or tables would flag for greater concern.
That is why the healthiest way to use this page is to compare scenarios. Try the expected plan, then a slightly deeper case, then a slightly longer case. If a small increase in either input moves the result more than you expected, you have learned something useful before entering the water. If nothing changes because the 3-minute minimum still applies, you have also learned something: the current formula has not crossed its first threshold yet.
Why simple calculators still help, even when the real world is more complex
Any calculator is a model: it takes a messy situation, reduces it to a few variables, and applies a rule consistently. That can be valuable even when the model is incomplete, because consistency helps you compare choices. The mathematical idea behind that process can be written very generally as “result equals a function of the inputs.”
Some tools are also built from several weighted pieces that are added together. That broader pattern is shown below. It is not the exact scuba formula used on this page, but it is a useful reminder that calculators often combine several influences into one output.
For diving, the lesson is simple: a small model can still teach a real relationship. Here the relationship is that more depth and more time both increase the estimated pause. That is a meaningful concept to understand, even though a certified diver should never confuse that concept with a full decompression algorithm.
Assumptions and limitations you should keep in mind
This estimator assumes a single, simplified profile. It does not know whether you were cold, working hard, diving repeatedly in one day, diving at altitude, using enriched air, or following agency-specific ascent guidance. It does not measure gas reserve, tank pressure, buddy separation, current, visibility, or emergency contingencies. It does not calculate staged decompression stops, tissue saturation, or no-decompression limits. In short, it is intentionally modest.
That is not a flaw if you use it correctly. It is a reason to use the page for learning, rough planning, and comparison, then lean on more authoritative tools for the final dive decision. If the result appears high, if the dive is operationally important, or if any parameter feels uncertain, slow down and verify the plan with training materials, a dive computer, and local expert judgment. Conservative interpretation is not a sign that the calculator failed; in diving, it is often the correct response to uncertainty.
- Use metres and minutes exactly as labeled. A feet-to-metres mistake can distort the estimate immediately.
- Treat the number as guidance for a 5 m pause, not a complete ascent plan.
- Remember that ascent control still matters. A stop duration is only one part of safer surfacing.
- Use your training and equipment first. This page is an educational helper, not a waiver of standard practice.
Estimated stop guidance
Copy status messages will appear here after you use the copy button.
Mini-game: Nail the Safety Stop
This optional canvas game turns the calculator's lesson into a fast skill challenge. Each round gives you a depth and bottom time. Your job is to guide the diver up the line, settle inside the glowing 5 m stop band, hold steady for the target time, and only then surface. The target hold in the game is shortened into seconds so a full run fits into about a minute, but the profile cards use the same depth-and-time idea as the calculator above. Smooth control scores better than frantic movement, and later rounds add current and buoyancy surges to keep the run lively.
Educational takeaway: the calculator rewards the same intuition as the game—deeper or longer profiles push the stop target upward, while a calm ascent helps you finish well.