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LOOT DROP & GACHA PROBABILITY CALCULATOR

Model exact drop chances, banner pulls, and pity thresholds for mobile and RPG games. Calculate the mathematical probability of obtaining rare items over $N$ attempts with cumulative probability distribution curves.

PROBABILITY PARAMETERS BINOMIAL MATH

PROBABILITY BREAKDOWN EXACT ODDS

CHANCE OF AT LEAST 1 DROP
39.50%
(60.50% chance of receiving 0 drops)
50% MEDIAN LUCK
69 Pulls
90% HIGH LUCK
230 Pulls
99% GUARANTEE
459 Pulls
Simulator ready. Click "Simulate Pulls" to run live rolls.

WEIGHTED RANDOM LOOT TABLE MANAGER (C# UNITY) 

using System.Collections.Generic;
using UnityEngine;

[System.Serializable]
public class LootItem
{
    public string itemName;
    [Range(0.01f, 100f)] public float dropWeight = 1.0f;
    public GameObject itemPrefab;
}

public class LootTableManager : MonoBehaviour
{
    public List lootPool = new List();

    public LootItem RollLoot()
    {
        float totalWeight = 0f;
        foreach (var item in lootPool) totalWeight += item.dropWeight;

        float roll = Random.Range(0f, totalWeight);
        float cumulative = 0f;

        foreach (var item in lootPool)
        {
            cumulative += item.dropWeight;
            if (roll <= cumulative) return item;
        }

        return lootPool[lootPool.Count - 1];
    }
}

UNDERSTANDING GACHA & LOOT DROP MATHEMATICS

The Gambler's Fallacy & Binomial Probability

A common misconception is that a 1% drop rate guarantees an item within 100 pulls. In reality, each attempt is an independent Bernoulli trial. The probability of failing 100 consecutive times at 1% is:

P(Failure) = (1 - 0.01)^100 = 36.6%

Therefore, after 100 pulls, you only have a 63.4% chance of getting at least one drop.

Why Games Implement Pity Systems

To protect players from statistical extreme outliers (the unluckiest 1% who might roll 400+ times without an item), modern games implement Hard Pity and Soft Pity mechanics.

Hard pity guarantees a 100% success rate on roll $N$, while soft pity progressively scales drop rates (e.g. +6% per pull after pull 74 in Genshin Impact) to smooth out player retention and satisfaction.