Define the reward you are trying to get
A chest can have several outcomes for the same item. The Ocean Mastery Chest, for example, lists one Forgehammer at 80% and two at 20%. The chance of receiving at least two in one opening is therefore 20%, while the expected number of Forgehammers per opening is 1.2. These answer different questions.
Use the right question
- Per-opening chance describes one ordinary draw. It does not grow because earlier independent draws failed.
- The chance of at least one success across n independent openings is 1 − (1 − p)ⁿ, where p is the per-opening probability.
- Expected quantity multiplies each outcome by its chance, then adds those averages. It can be fractional even though each real reward is a whole item.
- A guarantee counter, changing pool or draw without replacement needs a different model. An ordinary-roll chart cannot establish how such a system works.
A worked example
For a 20% target chance, five independent openings have a 67.232% chance of at least one success. They also have a 32.768% chance of none. Five openings is not a guarantee, even though the expected number of successful openings is one.
Choose a risk level before spending
The visualiser shows how many independent openings are needed to reach a chosen probability, including 90%, 95% and 99%. No finite number reaches an absolute 100% when the per-opening probability is below 100%. Compare the required attempts with your available chests or budget, and check for event-specific counters first.