How do I calculate the chance of getting a drop?

The chance of getting an item at least once over N runs is 1 minus the chance of getting none. Since each run fails with probability (1 minus the drop rate), the no-drop chance is (1 minus rate) to the power N, and one minus that is your odds of success.

Why isn't 40 runs at a 1-in-40 rate a guarantee?

Each run is independent, so doing 40 runs at a 2.5% rate gives only about a 64% chance — not 100%. Independent trials never add up to certainty, which is why long unlucky streaks happen even at the expected run count.

Does a dry streak improve my next drop chance?

No. With independent drops the game has no memory, so your next run is exactly the same percentage no matter how many times you have failed before. The only thing more runs change is the cumulative chance across the whole set.

What is the expected number of runs per drop?

It is one divided by the drop rate, so a 2.5% rate averages 40 runs per drop. This is a long-run average — some drops come far sooner and some far later, which is why the 90% and 99% confidence figures are higher than the average.

How many runs guarantee a drop?

Nothing short of a 100% rate truly guarantees it, but you can reach any confidence you like. The tool shows the runs needed for 90% and 99% confidence so you can plan a grind that almost always succeeds rather than one that only breaks even on average.

EVE Online Drop Rate & Probability Calculator

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Know your real EVE Online loot odds

Grinding the same site for a rare drop is far less predictable than it feels. This calculator gives you the actual probabilities — the chance of at least one drop, the chance of striking out, and how many runs you genuinely need to be confident — so you can decide whether to keep farming or accept the odds. It runs entirely in your browser.

How it works

Each run either drops the item with probability p or fails with probability 1 - p, independently of every other run. The chance of getting zero drops over N runs is the failure chance multiplied by itself N times, so the chance of at least one is its complement:

P(at least one) = 1 - (1 - p)^N

The average number of runs to the first drop follows a geometric distribution and equals 1 / p. To find how many runs you need for a confidence level C, invert the formula:

N = ceil( ln(1 - C) / ln(1 - p) )

Example and notes

At a 2.5% drop rate, the expected runs per drop is 40, but 40 runs only give about a 64% chance of success. To be 90% confident you need roughly 91 runs, and for 99% confidence about 182. Because each run is independent, a long dry spell never raises your odds on the next attempt — the rate stays fixed. Use the confidence figures, not the average, when you want a drop you can actually count on.