Pokemon Gold and Silver - Catch Rate Formula

E = int( ((B*4)-(A*2))*C/B+D)

A = Current HP, If A is greater than 255, A=int(int(A/2)/2)
B = Total HP, If B is greater than 255, B=int(int(B/2)/2)
C = Catch Rate (See below)
D = Status: If asleep, D=10, frozen, D=10, paralyzed, D=5, poisoned, D=5, burned, D=5, else D=0

If a random number from 0 through 255 is less than or equal to E, the Pokémon is caught. A higher number has a greater chance of success.

Finding the Catch Rate

The Catch Rate depends on the Pokémon, and the ball you're using. First, take a number called X (which is the Pokémon's rareness), and find the Pokémon you're battling in the chart. If at the end of the calculation you get a Catch Rate greater than 255, make it 255.

A wild Pokemon can be caught with a Ball even if it's currently using Dig or Fly. If the capture fails, that doesn't affect the wild Pokemon's two-turn attack.

X	Pokémon
3	Articuno, Zapdos, Moltres, Mewtwo, Raikou, Entei, Suicune, Lugia, Ho-oh
25	Clefable, Snorlax, Steelix, Scizor, Mantine, Skarmory
30	Chansey, Murkrow, Blissey
35	Ditto
45	Bulbasaur, Ivysaur, Venusaur, Charmander, Charmeleon, Charizard, Squirtle, Wartortle, Blastoise, Butterfree, Beedrill, Pidgeot, Nidoqueen, Nidoking, Vileplume, Poliwrath, Machamp, Victreebel, Golem, Farfetch'd, Dodrio, Gengar, Onix, Exeggutor, Hitmonlee, Hitmonchan, Lickitung, Tangela, Kangaskhan, Mr.Mime, Scyther, Jynx, Electabuzz, Magmar, Pinsir, Tauros, Gyarados, Lapras, Eevee, Vaporeon, Jolteon, Flareon, Porygon, Omanyte, Omastar, Kabuto, Kabutops, Aerodactyl, Dratini, Dragonair, Dragonite, Mew, Chikorita, Bayleef, Meganium, Cyndaquil, Quilava, Typhlosion, Totodile, Croconaw, Feraligatr, Ampharos, Bellossom, Politoed, Jumpluff, Aipom, Espeon, Umbreon, Misdreavus, Wobbuffet, Qwilfish, Heracross, Delibird, Houndoom, Kingdra, Porygon2, Stantler, Smeargle, Hitmontop, Smoochum, Elekid, Magby, Miltank, Larvitar, Pupitar, Tyranitar, Celebi
50	Wigglytuff, Dugtrio, Alakazam
60	Tentacruel, Rapidash, Magneton, Cloyster, Kingler, Electrode, Weezing, Rhydon, Seaking, Starmie, Girafarig, Gligar, Sneasel, Ursaring, Corsola, Donphan
65	Sudowoodo
70	Slowking
75	Raichu, Ninetales, Parasect, Venomoth, Golduck, Primape, Arcanine, Slowbro, Dewgong, Muk, Hypno, Marowak, Seadra, Lanturn, Togetic, Xatu, Azumarill, Yanma, Foretress, Granbull, Magcargo, Piloswine, Octillery, Tyrogue
90	Raticate, Fearow, Arbok, Sandslash, Golbat, Persian, Machoke, Haunter, Exeggcute, Furret, Noctowl, Ledian, Ariados, Crobat, Quagsire
100	Kadabra
120	Metapod, Kakuna, Pidgeotto, Nidorina, Nidorino, Gloom, Poliwhirl, Weepinbell, Graveler, Rhyhorn, Flaaffy, Skiploom, Sunflora, Teddiursa, Houndour, Phanpy
150	Clefairy, Cleffa
170	Jigglypuff, Igglybuff
180	Machop
190	Pikachu, Vulpix, Paras, Venonat, Psyduck, Mankey, Growlithe, Tentacool, Ponyta, Slowpoke, Magnemite, Doduo, Seel, Grimer, Shellder, Gastly, Drowzee, Voltorb, Cubone, Koffing, Chinchou, Pichu, Togepi, Natu, Marill, Pineco, Dunsparce, Snubbull, Shuckle, Slugma, Remoraid
200	Abra
225	Krabby, Horsea, Goldeen, Staryu, Unown, Swinub
235	Nidoran(f), Nidoran(m), Mareep, Sunkern
255	Caterpie, Weedle, Pidgey, Rattata, Spearow, Ekans, Sandshrew, Zubat, Oddish, Diglett, Meowth, Poliwag, Bellsprout, Geodude, Magikarp, Sentret, Hoothoot, Ledyba, Spinarak, Hoppip, Wooper

Now, find the ball you're using below.

Ball	Catch Rate =
Master Ball	X × 255 (in practice)
Poké Ball	X
Great Ball	X × 1.5
Ultra Ball	X × 2
Heavy Ball	X + Weight Bonus: -20: Any Pokémon not listed below goes here. 100 kg or less. 0: Arcanine, Machamp, Graveler, Dewgong, Cloyster, Exeggutor, Rhyhorn, Rhydon, Mewtwo, Forretress, Scizor, Ursaring, Kingdra, Donphan, Raikou, Entei, Suicune, Pupitar, Tyranitar, Ho-oh 100 to 200 kg. +20: Golem, Onix, Gyarados, Lapras, Dragonite, Mantine, Lugia 200 to 300 kg. +30: Snorlax, Steelix Greater than 300 kg.
Lure Ball	X × 3 if the Pokémon had been fished.
Friend Ball	X (Pokémon's happiness will be 200 if captured.)
Fast Ball	X × 4 if the Pokémon is Magnemite, Grimer, or Tangela. It was rumored that you can catch Raikou, Entei, and Suicune more easily with this ball, but this rumor is false.
Moon Ball	X × 4 if the Pokémon is Clefairy, Jigglypuff, Nidorino, or Nidorina (i.e., evolves with a Moon Stone). Because of a bug, this effect doesn't occur.
Park Ball	X × 1.5
Love Ball	X × 8 if Pokémon is of opposite gender of your Pokemon.
Level Ball	X × 2 if your Pokémon's level is higher. X × 4 if half your Pokémon's level, rounded down, is higher. X × 8 if 1/4 your Pokémon's level, rounded down, is higher.