In Brawl Stars, acquiring new Brawlers, cosmetics, and resources often comes down to opening Starr Drops. Understanding the mathematical probability behind these drops can help you manage your expectations and plan your resource collection. Unlike guaranteed progression systems, Starr Drops operate on a randomized "gacha" mechanic.
Official Rarity Probabilities
While Supercell occasionally adjusts drop rates during updates, the general consensus for Starr Drop rarities is as follows:
Legendary: ~2% – The most coveted drops, containing Hypercharges, Star Powers, or Legendary Brawlers.
Mythic: ~5% – Contains Gadgets, Mythic Brawlers, or high-tier cosmetics.
Epic: ~15% – Often contains Brawler Sprays, Emotes, or Epic Brawlers.
Super Rare: ~28% – Contains resources like Power Points and Bling.
Rare: ~50% – The most common drop, usually containing Coins or Power Points.
How the Math Works
This calculator uses the Binomial Distribution formula to determine your luck. Many players mistakenly believe that if a drop rate is 2% (1 in 50), opening 50 boxes guarantees a drop. This is the "Gambler's Fallacy."
The actual math calculates the probability of failure. For a Legendary drop (2% chance):
The chance of NOT getting a Legendary in one drop is 98% (0.98).
If you open 50 drops, the calculation is 0.98 ^ 50 = 0.364 (36.4%).
This means there is a 36.4% chance you get zero Legendaries.
Conversely, your chance of getting at least one is 100% - 36.4% = 63.6%.
Using the Calculator
To use this tool effectively:
Input Attempts: Enter the number of Starr Drops you plan to open (e.g., from the Brawl Pass or Mega Pig).
Select Rarity: Choose the tier you are hunting for. If you are calculating for a specific item inside a rarity (like a specific Brawler), select "Custom" and input that specific percentage (e.g., 0.1%).
Analyze: The result will show you the statistical likelihood of success.
What are "Expected Drops"?
The "Expected Number of Items" metric tells you the average outcome over a long period. If the Expected Number is 2.5, it means that on average, a player opening this many drops would get 2 or 3 items of that rarity. However, luck varies wildly for each individual session.
function updateCustomRate() {
var select = document.getElementById('raritySelect');
var customGroup = document.getElementById('customRateGroup');
var customInput = document.getElementById('customRate');
if (select.value === 'custom') {
customGroup.style.display = 'block';
customInput.focus();
} else {
customGroup.style.display = 'none';
customInput.value = select.value;
}
}
function calculateDropChance() {
// Get Inputs
var n = parseFloat(document.getElementById('dropCount').value);
var rateInput = document.getElementById('customRate').value;
var pPercent = parseFloat(rateInput);
// Validation
if (isNaN(n) || n <= 0) {
alert("Please enter a valid number of Starr Drops (greater than 0).");
return;
}
if (isNaN(pPercent) || pPercent 100) {
alert("Please enter a valid probability percentage between 0 and 100.");
return;
}
// Logic: Binomial Probability
// p = probability of success in decimal
// q = probability of failure (1 – p)
// Prob of 0 successes in n trials = q^n
// Prob of >= 1 success = 1 – q^n
var p = pPercent / 100;
var q = 1 – p;
var probFailure = Math.pow(q, n);
var probSuccess = 1 – probFailure;
var expectedValue = n * p;
// Formatting Results
var probabilityDisplay = (probSuccess * 100).toFixed(2) + "%";
var expectedDisplay = expectedValue.toFixed(2);
// Analysis Text Logic
var analysis = "";
if (probSuccess > 0.9) {
analysis = "Excellent odds! You are statistically very likely to get this drop.";
} else if (probSuccess > 0.5) {
analysis = "Good odds. It's more likely than not that you'll get at least one.";
} else if (probSuccess > 0.2) {
analysis = "Possible, but not guaranteed. Good luck!";
} else {
analysis = "Low odds. Don't get your hopes up too high with this many drops.";
}
if (n < 10 && pPercent 0.8) resultElement.style.color = "#53e053"; // Green
else if (probSuccess > 0.4) resultElement.style.color = "#ffbf00"; // Yellow
else resultElement.style.color = "#fe0000"; // Red
// Show Results
document.getElementById('results').style.display = 'block';
}