Loot Drop Probability Calculator

Multiplying drop rate by attempts gives Expected Drops — the average number of items you'd collect — but that's a different question from the probability of getting at least one. To find that probability correctly, this calculator computes the chance of failing every single attempt (missing the drop each time) and subtracts that from 1, since 'at least one success' and 'zero successes' are the only two mutually exclusive outcomes and must add up to 100%. This complement-rule approach correctly accounts for the fact that as attempts pile up, the chance of missing every single one shrinks multiplicatively, not linearly.

Closing the gap from a coin-flip 50% chance to a near-certain 99% chance requires disproportionately more attempts than reaching 50% did in the first place, because each additional attempt only shrinks your remaining miss-probability by a fixed fraction rather than a fixed amount. Mathematically, going from 50% to 99% typically takes more than 6 times as many attempts as reaching 50% did, at the same drop rate — a pattern inherent to probability, not specific to any one game's loot system.

No — Expected Drops is an average across many repeated farming sessions, not a guarantee for any single session. With a drop rate of, say, 5% and 20 attempts, Expected Drops equals exactly 1.0, but Chance of at Least 1 Drop in that scenario is only about 64%, meaning roughly one in three players farming exactly that many attempts will walk away with zero drops despite the 'average' being one.

Target Drop Count only affects Expected Runs for Target, which estimates how many attempts you'd need on average to collect that many copies of the item (target count divided by drop rate). It does not change Chance of at Least 1 Drop, Expected Drops, or the 50%/99% confidence figures for your entered Number of Attempts — those describe getting at least one drop within your specified attempt count, a separate question from farming multiple copies.

At low drop rates, doubling the rate roughly doubles your cumulative odds across a fixed number of attempts, because each individual attempt's miss-probability (very close to 100%) barely changes even when the drop rate itself doubles — the compounding effect across many attempts is what amplifies small rate differences. At higher drop rates this sensitivity flattens out, since the cumulative chance is already closer to its ceiling and has less room left to grow.