What is an Ichiban Kuji-style odds calculator?
An Ichiban Kuji-style draw is different from normal gacha because the pool changes after every ticket. When someone buys a ticket, that ticket is removed. If a target prize is still available, the odds can improve as non-target tickets disappear. If the target prize is drawn, it is gone.
This calculator uses a without-replacement model. Enter the current number of remaining tickets or prizes, the number of target prizes still left, and how many draws you plan to buy. It then estimates the chance of getting at least one target prize.
Use the current store display or remaining prize list when you can. If the board says 80 total tickets at the beginning but many have already been sold, the original number is no longer useful. The remaining pool is what matters.
Why this is different from normal gacha probability
miss probability = C(total - target, draws) / C(total, draws); success probability = 1 - miss probability The formula counts how many ways your draws can all come from non-target tickets, then compares that with all possible draw combinations. If your draw count is larger than the number of non-target tickets, missing every target is impossible, so the success probability becomes 100%.
This model assumes the remaining pool count is accurate and every remaining ticket is equally likely. It is not connected to any official prize brand, store, or lottery operator.
Example use cases
Two target prizes left in 80 tickets
With 2 target prizes and 80 total tickets remaining, buying 10 draws gives about a 23.58% chance of at least one target prize.
Late pool with one top prize left
If 1 target prize remains in 20 tickets, buying 5 draws gives a 25.00% chance. The pool is smaller, but one prize is still one prize.
When misses become impossible
If 3 target prizes and 2 non-target prizes remain, buying 3 draws guarantees at least one target because there are not enough non-target prizes to fill all draws.
Responsible use
Probability can help you understand risk, but it cannot guarantee a win. If you are buying pulls, boxes, packs, or prize tickets, set a budget first and avoid spending more than you can afford. A calculator is a planning aid, not a reason to chase losses or ignore your limit.
FAQ
Why does this calculator use without replacement?
Prize tickets are usually removed after each draw, so the odds change as the pool shrinks. A normal gacha formula would be less accurate for this format.
What if draws are greater than total tickets remaining?
The calculator will show an error. You cannot draw more tickets than remain in the pool.
Is this affiliated with any official brand?
No. This is an independent educational calculator and is not affiliated with any game, toy, anime, lottery, or prize draw brand.
Should I use original pool size or remaining pool size?
Use the remaining pool size whenever possible. Odds depend on what is still available at the time you draw.
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Helpful guides
How Gacha Probability Works
Learn how gacha probability works, why repeated pulls do not add up directly, and how to read at least-one-success odds.
Blind Box Odds Explained
Understand blind box odds, equal variant assumptions, secret item limits, duplicate risk, and how to compare boxes with resale prices.