Generic gacha math · user-supplied inputs

Gacha Reroll Success Probability Calculator

Model repeated account-start attempts as groups of independent rolls without estimating how long the process takes.

Quick answer

Example: At a 1% target rate with 20 rolls per reroll, one attempt succeeds about 18.2% of the time; ten independent attempts produce a much higher combined chance.

Success chance per reroll —
Success chance across all rerolls —
Total rolls represented —

What this calculator does

First, the tool calculates the chance that at least one target appears inside a single reroll batch. It then treats each identical reroll as another independent attempt and calculates the chance that at least one batch succeeds.

Grouping matters because “20 rolls in each of 10 rerolls” is easier to reason about operationally than a flat 200-roll total, even though the independent constant-rate probability is mathematically equivalent.

The result does not value time, accounts, or platform restrictions. It is a probability worksheet only; users supply the rate, batch size, and attempt count.

Formula

per reroll = 1 − (1 − rate) ^ rolls; overall = 1 − (1 − per-reroll chance) ^ attempts

Example: At a 1% target rate with 20 rolls per reroll, one attempt succeeds about 18.2% of the time; ten independent attempts produce a much higher combined chance.

FAQ

Is this different from one large pull session?

Under a constant independent rate the total probability is equivalent, but the grouped output shows per-reroll and overall odds separately.

Does the calculator estimate reroll time?

No. It uses rolls and attempt counts only.

Can the rate change between attempts?

Not in one calculation. Run separate scenarios if different attempts use different rates.

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