Poke Ball (1x)
Great Ball (1.5x)
Ultra Ball (2x)
Level Ball (1x – Neutral)
Level Ball (4x – High Level)
Heavy Ball (0 – Light)
Heavy Ball (+20 – Heavy)
Fast Ball / Lure Ball (Condition Met)
None
Asleep or Frozen (+10 bonus)
Paralyzed, Burned, or Poisoned (+5 bonus)
Estimated Catch Results
0%
Understanding Catch Mechanics in Pokemon Crystal
In the Johto region of Pokemon Crystal, the formula for catching Pokemon is significantly different from modern games. While modern titles use complex exponential formulas, Generation II relies on a combination of basic catch rates, fixed status bonuses, and HP ratios.
The Generation II Formula
The game determines your success based on a specific "Catch Value." The simplified logic used by the engine follows these steps:
Step 1: The Pokemon's base catch rate (e.g., 3 for Lugia, 255 for Pidgey) is multiplied by the Ball modifier (Ultra Ball = 2x).
Step 2: A fixed bonus is added for status conditions. Sleeping or Frozen targets are much easier to catch than those with Paralysis or Burns.
Step 3: The HP factor is applied. The lower the current HP relative to the maximum, the higher the final value.
Gen 2 Ball Glitches to Note
Pokemon Crystal is famous for several coding bugs regarding Poke Balls. The Love Ball, which should work on opposite genders, actually only works if the Pokemon are the same species AND the same gender. The Moon Ball was intended to work on Pokemon evolving with Moon Stones but erroneously only works on Pokemon that evolve with Burn Heals (which is none). This calculator assumes intended mechanics or standard multipliers unless otherwise specified.
Top Tips for Johto Trainers
Strategy
Effectiveness
False Swipe
Essential for bringing HP to 1 safely.
Sleep (Spore/Hypnosis)
Highest status bonus (+10 to the value).
Heavy Ball
Best for Snorlax and Lugia (adds to base rate).
function calculateCatchRate() {
var baseRate = parseFloat(document.getElementById('baseCatchRate').value);
var ballBonus = parseFloat(document.getElementById('ballType').value);
var hpMax = parseFloat(document.getElementById('hpMax').value);
var hpCurrent = parseFloat(document.getElementById('hpCurrent').value);
var statusBonus = parseFloat(document.getElementById('statusCondition').value);
if (isNaN(baseRate) || isNaN(hpMax) || isNaN(hpCurrent)) {
alert("Please enter valid numbers for HP and Catch Rate.");
return;
}
if (hpCurrent > hpMax) {
hpCurrent = hpMax;
document.getElementById('hpCurrent').value = hpMax;
}
// Gen 2 Catch Logic Simulation
// a = (((3 * MaxHP – 2 * CurrentHP) * CatchRate * BallModifier) / (3 * MaxHP)) + StatusModifier
var a = (((3 * hpMax – 2 * hpCurrent) * (baseRate * ballBonus)) / (3 * hpMax)) + statusBonus;
var probability = 0;
if (a >= 255) {
probability = 100;
} else {
// In Gen 2, if a 100) probability = 100;
if (probability 75) msg = "Great odds! You'll likely catch it in 1 or 2 throws.";
else if (probability > 25) msg = "Decent odds. Keep a stack of Great or Ultra Balls ready.";
else if (probability > 5) msg = "Tough catch. Recommend using Sleep status or more HP reduction.";
else msg = "Extremely difficult! Use Ultra Balls and status effects.";
document.getElementById('shakeProbability').innerText = msg;
}