None (1x)
Paralyzed, Poisoned, Burned (1.5x)
Asleep or Frozen (2.5x)
How to Calculate Catch Rate in Pokémon
Catching a Pokémon isn't just luck; it's a mathematical formula determined by the game's engine. Since Generation III, the core formula focuses on a value called 'a'. Understanding this helps you save expensive Ultra Balls and time during Legendary encounters.
The Catch Rate Formula
The modified catch rate a is calculated as follows:
a = (((3 * MaxHP – 2 * CurrentHP) * Rate * Ball) / (3 * MaxHP)) * Status
MaxHP: The total Hit Points of the Pokémon.
CurrentHP: The HP remaining at the time of the throw.
Rate: The species-specific base catch rate (e.g., Caterpie is 255, Mewtwo is 3).
Ball: The multiplier of the ball used (Ultra Ball is 2.0x).
Status: Sleep and Freeze give a 2.5x boost, while Burn, Paralyze, and Poison give 1.5x.
Example Calculation
If you are trying to catch a Pokémon with a Base Rate of 45 (like a typical starter) that has 10/100 HP and is Asleep, using an Ultra Ball:
Final Result: 210 / 255 = ~82.3% chance per throw.
Pro Tips for Catching Legendaries
1. The "False Swipe" Strategy: This move always leaves the opponent with at least 1 HP. In our formula, lowering HP from 100% to 1 HP nearly triples your catch chance.
2. Prioritize Status: Putting a Pokémon to sleep is significantly more effective (2.5x) than paralyzing it (1.5x).
3. Timer Balls: If a fight lasts more than 10 turns, the Timer Ball becomes the most powerful ball in the game with a 4.0x multiplier.
function calculateCatchRate() {
var maxHP = parseFloat(document.getElementById('maxHP').value);
var currentHP = parseFloat(document.getElementById('currentHP').value);
var baseRate = parseFloat(document.getElementById('baseCatchRate').value);
var ballBonus = parseFloat(document.getElementById('ballMultiplier').value);
var statusBonus = parseFloat(document.getElementById('statusMultiplier').value);
var resultDiv = document.getElementById('catchResult');
var percText = document.getElementById('percentageText');
var shakeText = document.getElementById('shakesText');
if (isNaN(maxHP) || isNaN(currentHP) || isNaN(baseRate) || maxHP maxHP) {
alert("Current HP cannot be greater than Max HP.");
return;
}
// The 'a' value formula (Gen 3-8 Standard)
var a = (((3 * maxHP – 2 * currentHP) * baseRate * ballBonus) / (3 * maxHP)) * statusBonus;
var catchProbability = 0;
if (a >= 255 || ballBonus >= 255) {
catchProbability = 100;
} else {
// Approximate probability for single throw
catchProbability = (a / 255) * 100;
}
// Cap at 100%
if (catchProbability > 100) catchProbability = 100;
if (catchProbability = 75) {
resultDiv.style.backgroundColor = "#d4edda";
resultDiv.style.color = "#155724";
} else if (catchProbability >= 30) {
resultDiv.style.backgroundColor = "#fff3cd";
resultDiv.style.color = "#856404";
} else {
resultDiv.style.backgroundColor = "#f8d7da";
resultDiv.style.color = "#721c24";
}
percText.innerHTML = catchProbability.toFixed(2) + "% Success Chance";
// Calculate expected throws (Geometric distribution 1/p)
var expectedThrows = 100 / catchProbability;
if (catchProbability = 100) {
shakeText.innerHTML = "Guaranteed catch! Gotcha!";
} else {
shakeText.innerHTML = "Statistically, you should catch it within " + Math.ceil(expectedThrows) + " throws.";
}
}