TnG - Drop Probability Calculator

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A little drop chance probability calculator for MMORPGs like WoW.

Calculator

Example: You want to get the Deathcharger mount from Baron Rivendare in WoW. We know that it has a 1% drop chance. That means that every time you kill the boss, you have a 1% chance of getting the mount. 1% on the first kill, and 1% on the 100th kill. The chance of dropping will always be 1%. However, over the course of 100 kills, you have a much higher probability of getting the mount. Not 100% though. In fact, it will never be 100% with a drop chance below 100%!

Explanation: Let us say you flip a coin. There is a 50% chance that it lands heads. You flip and get tails. Next time the chance is still 50%. Tails again. The next chance is still 50%. The past results do not affect the chance of the next result when it is a truely random scenario. But your chance over multiple attempts increases.

We are flipping our coin again. We know that we have a 50% chance of getting heads on any given toss, and it does not matter at all what results we have gotten before. Nonetheless, if we flip a coin 100 times it is very, very likely that we will get heads at least one of those times. The chance on the first toss is 50%, and on the 42nd toss it is 50% and on the 100th toss it is still 50%. But over the course of 100 tosses, the probability of getting heads is way more than 50%. (In fact, the chance that we will get heads at least once is 99.999999999999999999999999999921%).

So the more often we kill a boss, the more likely we are to see the loot that we want. (Despite the probability never being full 100%).

Using maths, we can learn that if we kill Baron Rivendare 100 times, we have a 63.4% probability of getting the mount drop at least once.

Note: The calculator uses some rounding after lots of decimal places, so it can give you a 100% probability due to rounding errors.