How is the chance calculated?
For a 1-in-N item the chance of missing it once is 1 - 1/N, so after n rolls the chance of having seen it at least once is 1 - (1 - 1/N)^n.
Roll Odds Calculator
Pick a documented item and a number of rolls. The maths treats each roll as independent at the game's listed base rate, which is the same assumption the in-game Index odds display implies.
Pick a target
Luck passes (2x, 4x) and the Luck II / III skills multiply the effective rate — the figures here use the base ladder, so treat them as a floor rather than a promise. Roll during a Global Booster window for the best practical odds.
Result
100.00%
chance of seeing Small Engine at least once in 100 rolls
- Average rolls needed
- 3
- Rolls for 50% confidence
- 2≈ 8s
- Rolls for 90% confidence
- 6≈ 24s
- Rolls for 99% confidence
- 12≈ 48s
Hitting the average does not mean the item is guaranteed — at that point you are only about 63% likely to have it. Plan against the confidence rows instead.
FAQ
Roll Odds Calculator FAQ
Does hitting the average number of rolls guarantee the item?
No. At the average you are only around 63% likely to have it. The table shows the counts for 50%, 90%, and 99% so you can plan against a real target instead of a coin flip.
Why do some items show no odds?
Because their ladder position has not been read from the game yet. Listing a made-up number would be worse than leaving it blank — this site only quotes odds that appear in footage or the Index.