In Generation 4 (Pokémon Diamond, Pearl, Platinum, HeartGold, and SoulSilver), the catch rate calculation determines your success in catching wild Pokémon. Unlike later generations, Gen 4 uses a specific formula involving four "shake checks" to decide if the Pokémon stays in the ball.
CurrentHP: The remaining health of the wild Pokémon.
Rate: The specific species catch rate (e.g., 3 for Dialga or Palkia).
BallMod: The multiplier for the ball used.
StatusMod: Multiplier for status ailments (Sleep and Freeze are the most effective).
Common Gen 4 Base Catch Rates
Pokémon Category
Base Catch Rate
Legendaries (Arceus, Giratina, Mewtwo)
3
Common Legendaries (Dialga, Palkia)
30
Starters and Rare Spawns
45
Mid-tier Evolutions
75 – 120
Common Pokémon (Rattata, Bidoof)
255
Optimizing Your Catch Success
To maximize your chances in Gen 4, follow these strategic steps:
False Swipe: Use the move False Swipe to leave the Pokémon at exactly 1 HP without knocking it out.
Status Effects: Use moves like Spore, Sleep Powder, or Sing. Sleep provides a 2x bonus, which is significantly better than Paralysis (1.5x).
Specialty Balls: Use Dusk Balls in caves or at night for a massive 3x multiplier, which is better than Ultra Balls (2x).
The Quick Ball Strategy: In Gen 4, a Quick Ball used on the very first turn has a 4x multiplier, making it the best non-Master Ball option for an immediate catch.
The Shake Check Logic
If the calculated value 'a' is less than 255, the game calculates a second value 'b'. It then performs four independent random checks. If all four checks pass, the Pokémon is caught. This is why you often see the ball shake once, twice, or three times before the Pokémon breaks free.
function calculateGen4Catch() {
var mHP = parseFloat(document.getElementById('maxHP').value);
var cHP = parseFloat(document.getElementById('currentHP').value);
var baseRate = parseFloat(document.getElementById('baseCatchRate').value);
var bMod = parseFloat(document.getElementById('ballModifier').value);
var sMod = parseFloat(document.getElementById('statusModifier').value);
var resultDiv = document.getElementById('catch-result');
var resultText = document.getElementById('result-text');
if (isNaN(mHP) || isNaN(cHP) || isNaN(baseRate)) {
resultDiv.style.display = 'block';
resultText.innerHTML = "Error: Please enter valid numerical values.";
return;
}
if (cHP > mHP) {
resultDiv.style.display = 'block';
resultText.innerHTML = "Error: Current HP cannot be greater than Max HP.";
return;
}
// Gen 4 Formula for 'a'
var a = (((3 * mHP – 2 * cHP) * baseRate * bMod) / (3 * mHP)) * sMod;
var probability = 0;
if (bMod === 255) {
probability = 100;
} else if (a >= 255) {
probability = 100;
} else {
// Gen 4 Shake Check Logic
// b = 65536 / (255/a)^0.25
var b = 65536 / Math.pow(255 / a, 0.25);
// Probability of passing one shake check is b / 65536
// Probability of catching is (b / 65536) ^ 4
probability = Math.pow(b / 65536, 4) * 100;
}
resultDiv.style.display = 'block';
var finalProb = probability.toFixed(2);
var shakes = "Expect several shakes!";
if (finalProb >= 100) {
shakes = "Guaranteed catch! The ball won't even shake.";
} else if (finalProb > 70) {
shakes = "High chance! It should stay in easily.";
} else if (finalProb < 5) {
shakes = "Very difficult! Expect many break-outs.";
}
resultText.innerHTML = "