Pokémon Catch Rate Calculator Gen 2

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Pokémon Gen 2 Catch Rate Calculator

Optimized for Pokémon Gold, Silver, and Crystal Mechanics

Legendaries are usually 3, common Mons 255.
Poké Ball / Friend Ball Great Ball / Park Ball Ultra Ball Master Ball
None Sleep / Freeze Paralysis / Poison / Burn

Catch Results

0%

How the Gen 2 Catch Formula Works

Catching Pokémon in Generation 2 (Gold, Silver, Crystal) follows a specific mathematical formula that differs significantly from later titles. While modern games use a more complex "shake check" system, Gen 2 relies on a simplified capture value designated as 'a'.

The Mathematical Core

The game calculates the value a using the following logic:

a = floor(floor((3 * MaxHP - 2 * CurrentHP) * CatchRate / (3 * MaxHP)) * BallModifier) + StatusModifier
  • Max HP & Current HP: Reducing a Pokémon's health increases 'a'. Ideally, you want the HP as low as possible (1 HP is best).
  • Catch Rate: A hidden value for every species. Lugia and Ho-Oh have a rate of 3, while Pidgey has a rate of 255.
  • Ball Modifier: Ultra Balls provide a 2x multiplier, while Great Balls provide 1.5x.
  • Status Modifier: Unlike later games where status is a multiplier, Gen 2 adds a flat value. Sleep and Freeze add 10, while other conditions add 5.

Gen 2 Base Catch Rate Reference

Pokémon Base Rate Difficulty
Lugia / Ho-Oh 3 Extremely Difficult
Raikou / Entei / Suicune 3 Extremely Difficult
Snorlax 25 Difficult
Scyther / Pinsir 45 Moderate
Rattata / Pidgey 255 Easy

Expert Tips for Johto Trainers

  1. False Swipe is King: Scizor or Farfetch'd using False Swipe to leave the target at 1 HP is the single best way to maximize your odds.
  2. The Power of Sleep: In Gen 2, Sleep is significantly more effective than Paralysis. Always prioritize putting the Pokémon to sleep before throwing balls.
  3. Kurt's Custom Balls: Be aware that in the original Gold/Silver/Crystal versions, some of Kurt's Apricorn balls were buggy. For example, the Moon Ball didn't actually work on Pokémon that evolved with Moon Stones. This calculator uses the standard intended multipliers.
function calculateGen2Catch() { var maxHP = parseFloat(document.getElementById('maxHP').value); var currHP = parseFloat(document.getElementById('currHP').value); var baseRate = parseFloat(document.getElementById('baseRate').value); var ballMod = parseFloat(document.getElementById('ballType').value); var statusMod = parseFloat(document.getElementById('statusEffect').value); // Validation if (isNaN(maxHP) || isNaN(currHP) || isNaN(baseRate) || maxHP maxHP) { currHP = maxHP; document.getElementById('currHP').value = maxHP; } // Master Ball Check if (ballMod === 255) { showPokemonResult(100, "Master Ball guaranteed catch!"); return; } // Gen 2 Formula: a = floor(floor((3*Max-2*Curr)*Rate/(3*Max))*Ball) + Status var step1 = Math.floor((3 * maxHP – 2 * currHP) * baseRate / (3 * maxHP)); var a = Math.floor(step1 * ballMod) + statusMod; var probability = 0; if (a >= 255) { probability = 100; } else { // Probability in Gen 2 is (a + 1) / 256 probability = ((a + 1) / 256) * 100; } if (probability 100) probability = 100; var message = ""; if (probability > 75) { message = "Excellent odds! You should catch it quickly."; } else if (probability > 30) { message = "Good odds. Might take a few tries."; } else if (probability > 10) { message = "Tough catch. Keep those Great/Ultra Balls ready."; } else { message = "Very difficult! Try lowering HP further or using Sleep."; } showPokemonResult(probability.toFixed(2), message); } function showPokemonResult(perc, msg) { document.getElementById('resultWrapper').style.display = 'block'; document.getElementById('catchProbability').innerText = perc + "%"; document.getElementById('catchMessage').innerText = msg; // Smooth scroll to result document.getElementById('resultWrapper').scrollIntoView({ behavior: 'smooth', block: 'nearest' }); }

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