Yellow Pokemon Catch Rate Calculator

In Yellow, every wild Pokemon has a hidden catch rate value, between 3 and 255. The higher that number, the more likely the Pokeball is to stay closed. Common Pokemon like Caterpie sit at 255. The legendary trio Articuno, Zapdos, and Moltres sit at 3, and Mewtwo at Cerulean Cave matches them at 3.

Generation I uses an older catch formula that does not multiply status and ball cleanly the way Gen III onward does. The big inputs are still HP percentage, status condition, and ball choice, but the math runs through a tighter coin-flip-style check rather than a stacked multiplier chain. Status is applied as a flat subtraction from a random catch-roll byte: Sleep and Freeze subtract 25, while Paralysis, Burn, and Poison each subtract 12 (per the pokered ROM at engine/items/item_effects.asm:222-231). The practical effect is similar to a 2x-ish multiplier for Sleep and a 1.5x-ish multiplier for the lesser statuses, but the underlying math is additive on the roll, not multiplicative on the catch rate. There is no critical capture mechanic to short-circuit a multi-shake check.

How to Increase Your Catch Chance

Without False Swipe in the move pool yet, you cannot guarantee 1 HP via a single move. The Gen I sequence is: apply Sleep first, chip HP carefully with weak resisted moves, then throw the best ball you have on hand. Sleep first is safer because the target stops attacking, so your low-level chip-damage Pokemon does not need to heal between turns.

1Apply Sleep for the catch bonus. Sleep is the strongest status condition for catching in Gen I. Putting the target down before chipping HP also means you cannot lose the encounter to a critical hit while you wear it down. Four primary sleep moves, ordered by accuracy:

SporeGrass

Power

—

Accuracy

100%

PP

15

Spore puts the target to sleep.

How to get it. Level-up move on Paras and Parasect. Both are wild on Mt. Moon and the Cerulean Cave entrance area. 100% accuracy makes Spore the most reliable sleep option in Gen I.

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ParasectParas

Sleep PowderGrass

Power

—

Accuracy

75%

PP

15

Sleep Powder puts the target to sleep, if it hits.

How to get it. Level-up move on the Bulbasaur line, Oddish line, and Bellsprout line. All three are accessible on Kanto routes. Cannot be learned via TM.

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VenusaurVileplumeVictreebelOddish

HypnosisPsychic

Power

—

Accuracy

60%

PP

20

Hypnosis puts the target to sleep, if it hits.

How to get it. Level-up move on the Drowzee line (Route 11 grass) and the Gastly line (Pokemon Tower in Lavender Town). Cannot be learned via TM.

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DrowzeeHypnoGengarHaunter

SingNormal

Power

—

Accuracy

55%

PP

15

Sing puts the target to sleep, if it hits.

How to get it. Level-up move on the Jigglypuff line and Clefairy line. Both are encounterable on Mt. Moon. Lower accuracy than the powder moves but easy to access early.

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JigglypuffWigglytuffClefable

2Chip HP carefully. With the target asleep you can use weak resisted moves to peel HP without risking a KO. Tackle from a low-level Pokemon, a not-very-effective move into a resistant target, or a single-target move from a much weaker attacker. Watch the HP bar and stop while the Pokemon is still in the red.

3Throw the best ball you have. Gen I has only five ball types: Poke Ball, Great Ball, Ultra Ball, Master Ball, and Safari Ball. Walk through the questions below to pick the right one for your situation.

Gen I has no situational multiplier balls (those debut in Gen III). Walk through these two questions and stop at the first YES. If neither applies, throw the strongest plain ball you have.

1

Are you inside the Safari Zone?

YES→Safari Ballin Safari Zone only

Replaces every other ball while you are inside the Safari Zone. The only ball you can throw there. Catch rate behaves like a Poke Ball mechanically but the Safari Zone has its own bait and rock mini-game in place of weakening.

2

Is this a critical legendary you want to lock in without risk?

YES→Master Ballguaranteed catch

One per game, given by the Silph Co. president after defeating Giovanni. Always succeeds with zero RNG. Most players save it for Mewtwo at Cerulean Cave or whichever legendary they care most about not missing.

★

If no question above applied

DEFAULT→Throw the strongest plain ball in your bag

Ultra Ball2x bonus

Great Ball1.5x bonus

Poke Ball1x (no bonus)

Use the strongest tier you have. Ultra Ball is best, Great Ball is mid-tier, Poke Ball is the basic fallback when nothing else is available.

Skipping the Sleep step is the single biggest catch-rate cost in Gen I, since there is no critical capture and no situational ball to make up for missing the multiplier. The full sequence is apply Sleep, chip HP, then throw an Ultra Ball or save the Master Ball for the encounter that needs it most.

Yellow keeps the same Gen I catch formula as Red and Blue, with one Master Ball from Silph Co. after Giovanni. Yellow is unique for letting you obtain all three original Kanto starters across the storyline without trading. The trickiest catches still come from the legendary trio (Articuno, Zapdos, Moltres) and Mewtwo at Cerulean Cave, all sitting at the catch-rate floor of 3.