How to use it
- Choose percent or 1 in N and enter the drop rate from the game’s wiki or data mining.
- Enter how many tries you plan or have already done.
- Set the target chance, such as 90 % or 99 %.
- Read the chance of at least one drop and how many tries the target needs.
The formulas
- At least one drop in n tries: 1 − (1 − p)ⁿ.
- No drop: (1 − p)ⁿ.
- Expected drops: n × p.
- Tries for a target t: ⌈ln(1 − t) ÷ ln(1 − p)⌉.
- Average tries per drop: 1 ÷ p.
Worked example
A 1 % drop over 100 kills, target 90 %:
- no drop: 0.99¹⁰⁰ = 36.6 %, so at least one: 63.4 %;
- expected drops: 100 × 0.01 = 1;
- for 90 %: ln 0.1 ÷ ln 0.99 = 229.1, rounded up to 230 kills;
- for 50 %: ln 0.5 ÷ ln 0.99 = 69 kills, while the average is 100.
Handy numbers
| Drop rate | 50 % | 90 % | 99 % |
|---|---|---|---|
| 10 % | 7 | 22 | 44 |
| 1 % | 69 | 230 | 459 |
| 1 in 512 | 355 | 1,178 | 2,356 |
| 0.1 % | 693 | 2,302 | 4,603 |