None (1x)
Sleep or Freeze (2x)
Paralyze, Burn, or Poison (1.5x)
Catch Results
0%
How the Fire Red Catch Rate is Calculated
In Pokémon Fire Red and Leaf Green (Generation III), catching a Pokémon isn't just luck. It's a mathematical formula processed by the GameBoy Advance hardware. This calculator replicates that exact logic to help you decide if you should throw an Ultra Ball or risk one more hit.
The Capture Formula
The game first calculates a value called 'a' using your current parameters:
a = (((3 * Max HP – 2 * Current HP) * Catch Rate * Ball Bonus) / (3 * Max HP)) * Status Bonus
The "Shake Check" Mechanic
If the value 'a' is 255 or higher, the Pokémon is caught instantly. If not, the game performs "shake checks." It calculates a second value 'b':
b = 65536 / (255 / a)^0.25
The game generates a random number four times. If all four numbers are less than 'b', you've successfully caught the Pokémon! This is why you often see the ball shake once, twice, or three times before the Pokémon escapes.
Pro Tips for Catching Legendaries
The 1 HP Strategy: Using the move False Swipe is critical. It ensures the Pokémon remains at 1 HP, maximizing the first part of the formula.
Status Matters: Sleep and Freeze provide a 2x multiplier, which is significantly better than the 1.5x multiplier from Paralysis or Poison.
Base Catch Rates: Most Legendaries in Fire Red (like Articuno, Zapdos, Moltres, and Mewtwo) have a base catch rate of 3. This makes them extremely difficult to catch even at low HP.
Base Catch Rate Reference Table
Pokémon Type
Examples
Base Rate
Common Starters
Pidgey, Rattata, Caterpie
255
Mid-Tier
Pikachu, Jigglypuff
170-190
Rare / Evolved
Snorlax, Lapras, Arcanine
25-45
Legendary
Mewtwo, Moltres, Entei
3
function calculateFireRedCatch() {
var maxHP = parseFloat(document.getElementById('fr_max_hp').value);
var currHP = parseFloat(document.getElementById('fr_curr_hp').value);
var baseRate = parseFloat(document.getElementById('fr_base_rate').value);
var ballBonus = parseFloat(document.getElementById('fr_ball_type').value);
var statusBonus = parseFloat(document.getElementById('fr_status').value);
if (isNaN(maxHP) || isNaN(currHP) || isNaN(baseRate) || maxHP <= 0 || currHP maxHP) {
alert("Current HP cannot be higher than Max HP.");
return;
}
// Capture Value 'a'
// Formula: a = (((3 * Max HP – 2 * Current HP) * Catch Rate * Ball Bonus) / (3 * Max HP)) * Status Bonus
var a = (((3 * maxHP – 2 * currHP) * baseRate * ballBonus) / (3 * maxHP)) * statusBonus;
var finalProb = 0;
var resultText = "";
if (a >= 255) {
finalProb = 100;
resultText = "This is a guaranteed catch! The Pokémon cannot escape under these conditions.";
} else {
// Calculate 'b' for shake checks
// b = 65536 / (255 / a)^0.25
var b = 65536 / Math.pow((255 / a), 0.25);
// The probability of catching is ( (b+1) / 65536 ) ^ 4
// Because 4 random numbers must be less than b
var shakeProb = (Math.floor(b) + 1) / 65536;
finalProb = Math.pow(shakeProb, 4) * 100;
if (finalProb < 0.1) {
resultText = "Extremely difficult! You'll need a lot of luck or a better strategy.";
} else if (finalProb < 10) {
resultText = "Tough catch. Consider lowering its HP more or using a status condition.";
} else if (finalProb < 40) {
resultText = "Decent chance. Expect the ball to shake a few times!";
} else {
resultText = "High probability! You should be able to catch it within a few tries.";
}
}
document.getElementById('fr_result_container').style.display = 'block';
document.getElementById('fr_percentage').innerText = finalProb.toFixed(2) + "%";
document.getElementById('fr_details').innerText = resultText + " (Capture Value a: " + Math.floor(a) + ")";
// Scroll to result
document.getElementById('fr_result_container').scrollIntoView({ behavior: 'smooth', block: 'nearest' });
}