Understanding how catch rate is calculated is essential for optimizing your strategy when attempting to capture rare or legendary creatures in monster-taming games. While the specific mechanics can vary slightly between game generations, the core mathematical formula relies on four primary variables: Health Points (HP), the Species' Base Rate, the Ball Multiplier, and Status Conditions.
The Core Calculation Formula
The standard formula used to determine if a capture is successful calculates a "Modified Catch Rate" (often denoted as a). The game then generates a random number; if the random number is lower than the calculated threshold, the capture is successful (or a "shake" check is passed).
HP Factor: Lowering the target's health is the most effective way to increase your odds. A target at 1 HP provides nearly 3x the catch probability compared to a target at full health.
Base Capture Rate: Every species has an innate "catch difficulty" ranging from 3 (hardest, e.g., Legendaries) to 255 (easiest, e.g., common early-game creatures).
Ball Multiplier: Different capture devices apply a multiplier. Standard devices offer a x1.0 multiplier, while advanced ones can offer x2.0, x3.5, or even x4.0 under specific conditions (like being in a cave or on the first turn).
Status Multiplier: Applying status effects significantly boosts the modified rate. Sleep and Freeze usually offer the highest bonus (x2.5), while Paralysis, Poison, and Burn offer a smaller bonus (x1.5).
Understanding the Probability
Once the "Modified Catch Rate" (a) is calculated, the probability of capture per throw is roughly determined by comparing a to the maximum byte value (255). If a is 255 or higher, the capture is guaranteed.
For values under 255, the game typically performs four "shake checks." The probability of the ball shaking once is approximately (a/255)^0.25 (in newer generations). For the capture to stick, all four checks must pass. Our calculator above simplifies this into a final percentage chance for your convenience.
Strategic Tips
To maximize your catch rate:
Use a move like "False Swipe" to safely lower the target to exactly 1 HP.
Apply a Sleep or Freeze status condition immediately.
Select the best Ball for the situation (e.g., use Dusk Balls at night).
function calculateCatchProbability() {
// 1. Get DOM elements
var maxHpInput = document.getElementById('maxHP');
var currHpInput = document.getElementById('currentHP');
var baseRateInput = document.getElementById('baseRate');
var ballSelect = document.getElementById('ballBonus');
var statusSelect = document.getElementById('statusBonus');
var resultArea = document.getElementById('result-area');
// 2. Parse values
var maxHP = parseFloat(maxHpInput.value);
var currHP = parseFloat(currHpInput.value);
var baseRate = parseFloat(baseRateInput.value);
var ballBonus = parseFloat(ballSelect.value);
var statusBonus = parseFloat(statusSelect.value);
// 3. Validation
if (isNaN(maxHP) || isNaN(currHP) || isNaN(baseRate)) {
alert("Please enter valid numbers for HP and Base Rate.");
return;
}
if (currHP > maxHP) {
alert("Current HP cannot be higher than Max HP.");
return;
}
if (currHP 255) {
modifiedRate = 255;
}
// 6. Calculate Probability
// Using the Shake Check approximation from Gen 3/4 mechanics which is standard for calculators.
// P = ( (a / 255) ^ 0.75 ) ? No, simplified formula is often P = a/255 for linear,
// but the actual mechanic is 4 shake checks.
// Probability of 1 shake = (65536 / ( (255/a)^0.1875 ) ) / 65536
// Simplified approximation for web: P = (modifiedRate / 255) * 100.
// However, to be more accurate to the "feel" of the game (Generation 6+):
// If a >= 255, 100%.
// Else, shake probability 'b' = 65536 * (modifiedRate/255)^0.25
// Catch Probability = (b/65536)^4
var catchProbPct;
if (modifiedRate >= 255) {
catchProbPct = 100;
} else {
// Gen 6+ Formula Approximation
var b = 65536 * Math.pow((modifiedRate / 255), 0.25);
var pShake = b / 65536;
var pCatch = Math.pow(pShake, 4);
catchProbPct = pCatch * 100;
}
// 7. Display Results
displayResult(modifiedRate, catchProbPct);
resultArea.style.display = 'block';
}
function displayResult(modRate, probPct) {
// Update A-Value
document.getElementById('resModRate').innerText = Math.floor(modRate);
// Update Percentage
var finalPct = probPct > 100 ? 100 : probPct;
document.getElementById('resProb').innerText = finalPct.toFixed(2) + "%";
// Update Expected Throws (1 / probability)
var throws = 0;
if (finalPct >= 100) {
throws = 1;
} else if (finalPct <= 0) {
throws = "Infinite";
} else {
throws = Math.ceil(100 / finalPct);
}
document.getElementById('resThrows').innerText = throws;
}