What this calculator can tell you
It estimates the chance of seeing at least one success across a chosen number of attempts, assuming each attempt is independent and the probability never changes. It does not predict your next result or connect to your Roblox account.
The default 1-in-100 chance is a worked example. It is not an official horse, egg, or trait probability. If your game does not show a reliable chance, the result can only be a hypothetical scenario.
A worked example
With a 1-in-100 chance, 100 attempts produce approximately a 63.4% chance of at least one success. There is still approximately a 36.6% chance of no successes. About 69 attempts reach a 50% chance; 299 reach at least 95%.
The formula
Let X be the denominator in “1 in X,” and n the attempt count. The probability is:
The chance of failing one attempt is 1 − 1/X. Multiply that chance across n independent attempts to get the chance of failing every time, then subtract from 1. For a 50% target, the attempt count is rounded up from log(0.5) / log(1 − 1/X). A guaranteed 1-in-1 outcome takes one attempt.
When the model does not apply
- A pity counter changes the chance after failures.
- Luck boosts, egg types, or events change between attempts.
- Several traits are linked instead of rolled independently.
- The input is a badge award rate rather than a per-attempt chance.
Past failures do not improve the next attempt under this model. Keep any real in-game counters or modifiers separate. See rarities and traits for the distinction between confirmed tiers and unverified rates.