How the dry calc works out your luck
Every kill is its own roll. Missing a drop on one kill does nothing to the next, so the maths is short:
- Chance of no drop on one kill: 1 − 1/X, where X is the rate.
- Chance of no drop in N kills: that number multiplied by itself N times.
- Chance of at least one drop: 1 minus the line above.
The "drier than" figure is the same number turned around. If 13.5% of players at your kill count still have nothing, you are drier than the other 86.5%.
What dry looks like at each multiple of the rate
| Kills done | Chance of at least one | Players still dry |
|---|---|---|
| 1× the rate | 63.2% | 36.8% |
| 2× the rate | 86.5% | 13.5% |
| 3× the rate | 95.0% | 5.0% |
| 5× the rate | 99.3% | 0.7% |
These figures barely change between a 1/100 drop and a 1/10,000 drop, so they make a good rule of thumb. The main thing to take from the first row: reaching the drop rate is not the point where you "should" have it. More than a third of players get there empty-handed.
Kills needed for a given chance
Turn the formula around and you get kill counts. For any rare drop, multiply the rate by the figure in the middle column:
| Chance you want | Multiply the rate by | Kraken tentacle (1/400) |
|---|---|---|
| 50% | 0.69 | 277 kills |
| 75% | 1.39 | 554 kills |
| 90% | 2.30 | 920 kills |
| 99% | 4.61 | 1,840 kills |
So half of all players have a tentacle from the Kraken by kill 277, and one player in a hundred is still waiting at 1,840.
Examples from real drop tables
- The dragon pickaxe drops at 1/1,000 from the King Black Dragon. At 2,000 kills, 13.5% of players have not had one, while 59% have had two or more.
- Many boss pets, including Vorki, Prince Black Dragon and the Kraken pet, are 1/3,000. Half of players have one by about 2,080 kills; at 9,000 kills about 5% are still without.
- The Trident of the Seas from the Kraken is 1/512. By kill 512, 63% of players have it.
No pity timer, so nothing is ever "due"
There is no hidden counter that makes a drop more likely the longer you go without it. Your next kill has the same odds as your first. That is why the calculator talks about chances and percentiles rather than a date your item is due.
A few rewards do not fit the simple model. In raids such as the Chambers of Xeric, your chance per run depends on points and team size, and some drops have different rates depending on how you kill the monster. For those, work out your own chance per attempt from the wiki drop table and enter that as the rate.
The expected number of drops is just kills divided by the rate. It is an average across everyone, not a promise, and a long dry streak is normal on any rare item. Planning a grind for profit? The OSRS money making list shows what each boss is worth per hour while you wait.