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A little drop chance probability calculator for MMORPGs like WoW.

Calculator

Drop Chance In Percent:
Number Of Runs:

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. 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 on a 1% drop chance, 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.