From Bulbapedia, the community-driven Pokémon encyclopedia.
Pokémon breeding is a method of obtaining a new Pokémon by producing and hatching an Egg. In the anime, it also refers to Pokémon grooming and caretaking.
In the games
How to breed
Pokémon can be bred by leaving two compatible Pokémon at the Pokémon Day Care in Generation II and beyond, located on Route 34 in Johto, Route 117 in Hoenn, Four Island in the Sevii Islands, Solaceon Town in Sinnoh and Route 3 in Unova. Two Pokémon are compatible if they are of the same species, or share at least one Egg group, and are of opposite genders (see below); alternatively, breeding is usually still possible as long as one of them is Ditto, even if the other parent is genderless. legendary Pokémon (excluding Phione and Manaphy), baby Pokémon, Unown, Nidorina and Nidoqueen cannot breed whatsoever. Pokémon with gender unknown (besides the aforementioned Pokémon) can only breed with Ditto.
- Same species, different ID numbers
The chance of getting an Egg is 69.3% (has a value of 70).
The old man in the Day Care will say: "The two seem to get along very well."
- Same species, same ID numbers
The chance of getting an Egg is 49.5% (has a value of 50).
The old man in the Day Care will say: "The two seem to get along."
- Different species, different ID numbers
The chance of getting an Egg is 49.5% (has a value of 50).
The old man in the Day Care will say: "The two seem to get along."
- Different species, same ID numbers
The chance of getting an Egg is 19.8% (has a value of 20).
The old man in the Day Care will say: "The two don't seem to like each other."
- Different Egg groups, same genders or Undiscovered group
The Pokémon are incompatible and therefore will not make an Egg.
The old man in the Day Care will say: "The two prefer to play with other Pokémon than each other."
Receiving the Egg
When there are two compatible Pokémon in the Day Care, for every 256 steps that the player takes, the game will decide whether the old man has found an Egg, with chances depending on the exact compatibility of the two Pokémon. If there was an Egg produced, the old man will be outside (Generation II), out of line with the fence (Generation III), facing the road (Diamond, Pearl, and Platinum), face left or right instead of down and call the player over the Pokégear (HeartGold and SoulSilver), or call the player from a distance when passing by on the road below (Generation V). However, in Black and White, the old man will not call out to the player if the player's party is full, even if he has found an Egg. The man will hand the player an Egg if he or she replies to his question with "Yes" and has an empty slot in the party, and permanently keep the Egg if the player responds "No". If the player selects "Yes" but does not have a spare slot, the man will keep it until the player returns and offer it again. Otherwise, there is no way to refuse the Egg and receive it later.
What will hatch
After walking around for a while, the Egg will hatch into a level 5 (Generation II and III) or level 1 (Generation IV and V) first-stage Pokémon of the female species' (or non-Ditto parent's) evolutionary chain.
However, there are two pairs of Pokémon species where the male and female are treated as different Pokémon. In these cases, an Egg produced by the female species may hatch into either the male or female variant; The pairs are the following:
There are also some Pokémon which will produce variable Eggs. The Pokémon that is in these Eggs will depend on whether or not the parents held a certain type of incense while breeding.
The time it takes for Eggs to hatch depends on the Pokémon's species' required number of Egg cycles. Magikarp is the fastest hatching Pokémon with the fewest Egg cycles required for hatching. Some baby fairies, such as Cleffa, Pichu and Igglybuff hatch quickly as well. Besides these, most Pokémon take considerable time to hatch. Rare and powerful Pokémon, like Dratini, Bagon, Beldum, Larvitar, Gible, Aerodactyl, Snorlax, Spiritomb, Chansey, and Eevee, among others, take a long time to hatch due to high numbers of Egg cycles required for hatching.
"Time" is actually determined by Egg cycle completion, which is determined by in-game steps or biking. An Egg cycle is a counted number of steps that activate breeding related programs in the game. One Egg cycle lasts 256 steps in the third generation and 255 steps in the fourth generation. After 255/256 steps are taken, the game recognizes the completion of the cycle and does a few things; the step counter for the cycles is reset to zero, the game randomly decides if an Egg is to be found at the Day Care (if compatible Pokémon are present in the Day Care at the time), and all (or only a few) Eggs currently in the player's team are taken down one Egg cycle count. If the Egg cycle count for an Egg reaches zero or a negative number, the Egg will begin to hatch. If an Egg hatches, the game stops subtracting an Egg cycle count from the rest of the Eggs in the team. Due to this, since the third generation, no two Eggs can hatch at the same time.
The other way to reset the game counter is to receive an Egg from the Day-Care Man (or in the Manaphy Egg's case, from the Mystery Gift delivery man in the Poké Mart). Every time an Egg is received, the game automatically resets the Egg cycle step counter to zero, and counts as another Egg cycle completion. This can effectively cut 254 (255 in the third generation) steps off the Egg hatching process for every Egg accepted from the Day-Care Man (the Egg must be accepted, not rejected or denied due to a full team to reset the step counter). Although this detracts an Egg cycle from the Eggs, any Eggs ready to hatch upon this type of Egg cycle completion will be denied the ability to hatch until the next Egg cycle completion by steps, perhaps due to the dialogue between the player and the Day Care man following the pickup of an Egg.
For example, a Gligar Egg requires 21 Egg cycles to hatch, a minimum of 5355 steps if not interrupted by an Egg hatching or Egg pickup. After each Egg cycle is completed, this Egg will drop one Egg cycle count, down to 20, then 19, then 18, so on and so forth until the Egg count hits zero. If nothing restricts the Egg from hatching, the Egg will hatch into Gligar. If it is restricted, it will continue dropping into the negative numbers from the Egg cycles, and will continue to try hatching if the Egg is stopped from another Egg pickup.
There are ways to speed this system up. Riding a bicycle (for example) would reduce the Egg's actual hatching time by traveling quickly, raising the step count faster, and completing Egg cycles faster. Pokémon Ruby, Sapphire, and Emerald allow players to use the Mach Bike, which is twice as fast as the Acro Bike. Pokémon FireRed and LeafGreen gives players a harder time hatching their Eggs due to the Bicycle having the same speed as the Running Shoes. Additionally, in Pokémon Emerald and onwards, if any Pokémon with Flame Body or Magma Armor is anywhere in a player's party, it doubles the Egg cycle count reduction, effectively halving the steps needed to hatch the Egg. In the Gligar example, the Egg would start at 21, and with Slugma in the party, the Egg would drop 2 Egg cycle counts after each Egg cycle, from 21 to 19 to 17 and so on. This feature became standard in Generation IV. Also, if the player finds a sandy slope the players can hold the "up" button therefore trying to go up. The player will fail unless he or she is not on the bicyle's faster speed, counting as one step. If the player somehow holds this button down for an extended period of time, the Egg would eventually hatch. The final way to speed up Egg hatching is to use the Pokétch step counter in Pokémon Diamond, Pearl, and Platinum to attempt to pick up an Egg from the Day-Care Man one step after an Egg cycle completes. This will cut 254 steps off the hatching process (this particular Egg count reduction may not be affected by the Flame Body/Magma Armor Ability, and may only ever reduce the Egg cycle count by one). In the Gligar example, if the player had the Gligar Egg and biked for exactly 255 steps after receiving the Egg, the Egg would reduce one Egg cycle count (down to 20), and the Egg cycle step counter would reset. If the player could then reach the Day-Care Man with only one step, the Egg cycle step counter would read one step taken. Then, the player could receive an Egg from the Day-Care Man, and the Egg cycle step counter would be forced back to zero, and the Egg cycle would reduce again for the first Gligar Egg, reducing the Egg cycle count for the Gligar to 19 in only 256 steps, cutting out 254 steps otherwise.
Passing moves down
The moves obtained by a Pokémon when hatching are as follows:
- The Pokémon will start with any moves that it would learn as a "Start" move in its learnset (In Generation II and Generation III, they learned all moves that are level 5 and below in their learnset.).
- The Pokémon will start with any moves that it would learn by leveling up only if both parents know the move. This does not apply to moves that later evolutions can learn (such as Breloom's Mach Punch, which Shroomish cannot learn for obvious reasons).
- The Pokémon will start with any TM or HM moves (and in Crystal, Move Tutor moves) that the father knows and the baby can also learn by machine.
- The Pokémon will start with any Egg moves that the baby can learn and the father knows.
The moves will take precedence in the order listed, and if there are more than four moves to learn, the moves will start being overwritten much like when leveling up at the Pokémon Day Care.
From Pokémon Emerald and onwards, there is a specific method to produce a Pichu that knows the move Volt Tackle: When breeding a Pikachu or Raichu holding a Light Ball, the offspring Pichu will know the move Volt Tackle. The parent need not know the move itself, and is not required to be of any specific gender; however, a male Pikachu or Raichu has to breed either with a female counterpart or with Ditto so that the offspring is, in fact, a Pichu.
A Pokémon's individual values are also passed down. This is determined differently between Generation II and Generation III games.
In Generation II games, the baby inherits its stats from the parent of the opposite gender, unless one parent is Ditto, and in that case it inherits the stats from Ditto. The Defense IV (Individual Value) is passed, and also either the Special IV or the Special IV plus or minus 8 (plus for values in the 0-7 range; minus for values in the 8-15 range); the Special IV has a 50% chance of remaining the same. Attack and Speed IVs are determined entirely at random, whereas HP is determined by the IVs of the other four stats, using the same formula for wild Pokémon. The probability of a Pokémon inheriting all of its opposite-gender parent's IVs is therefore 1/512.
When determining if two Pokémon are compatible, their Egg group is only one criterion. For Pokémon of the same Egg group, if the Defense IVs are the same, and either the Special IVs are the same or 8 off, they are incompatible. This is due to the high likelihood of a family relation, hence the inability to breed.
In Pokémon Ruby, Sapphire, FireRed and LeafGreen, exactly three of the baby's IVs are inherited from either parent (which is to say that one parent can contribute a number of IVs that ranges from 0 to 3, and its mate will contribute the remaining number of IVs from other stats). The other three are determined at random, in such a way that it is possible that more of the offspring's IVs will coincide with those of its parents.
In Pokémon Emerald, the process is similar but more complicated. First, a random IV is passed from one of the parents to the baby. Afterwards, a random IV of any stat, other than HP, is inherited from either parent to the baby. If this IV is from the same stat as the first IV (not necessarily the same IV value, depending on whether or not the same parent passed it on), it will override it. Finally, another random IV of any stat other than HP and Defense, is passed from one of the parents to the baby. This IV will override any of the previous two if it is from the same stat. The remaining stats (a number ranging from 3 to 5) are determined at random, again with the possibility of one or more IVs coinciding with those of the parents.
Inheriting IVs in Pokémon Diamond and Pearl is determined in the same way as in Pokémon Emerald.
In HeartGold and SoulSilver, the baby will inherit three IVs, each from a different stat and from a random parent. In addition, a new mechanic was added to breeding, where if either or both parents holds an EV item, instead, the baby will receive the IV of the corresponding stat from one of those parents and the baby will then inherit two other different random IVs, each from a random parent. For example, if a parent is holding the Power Anklet, the baby will inherit a Speed IV from that parent, and it will also inherit two other different IVs from its parents, for example, Attack and Special Defense. As another example, if one parent holds a Power Anklet and the other parent holds a Power Weight, the baby will inherit either a Speed IV from the first parent or an HP IV from the second parent, and it will also inherit two different IVs from its parents other than Speed or HP.
Inheriting IVs in Generation V is determined in the same way as in Pokémon HeartGold and SoulSilver.
Another change introduced in Emerald is the ability to inherit nature, which also influences stats. If the mother (or Ditto) is holding an Everstone, the baby has a 50% chance of inheriting that Pokémon's nature. It should be noted that Ditto always acts as the "mother" in a breeding match-up, so in Emerald, a female breeding with a Ditto does not have a better chance of passing down natures to its offspring; the Ditto does.
In Generation IV, in Diamond, Pearl, and Platinum, inheriting natures remains the same as in Emerald. However, in the Johto remakes, HeartGold and SoulSilver, inheriting nature was changed a little. Whichever Pokémon is holding an Everstone will pass down its nature, regardless of gender, or whether it is breeding with a Ditto. Another minor change that is present in all Generation IV games, is that the passing on of natures via an Everstone will not work if the Pokémon are from different real-world countries (e.g. Argentina and Spain). This restriction is lifted in Generation V. 
From Generation V, female Pokémon with Hidden Abilities have a 60% chance of passing on the Hidden Ability to their offspring when bred with a male Pokémon from the same Egg group. For example, if a female Darmanitan with Zen Mode bred with a male Simisage, the offspring Darumaka may have Inner Focus instead of the usual Hustle, and would evolve into a Darmanitan with Zen Mode (instead of Sheer Force).
Hidden Abilities cannot be passed down from male or genderless Pokémon, and will not be passed down if the female was paired with a Ditto.
Breeding for Shininess
In Generation II, a player can breed for "Shininess." Due to the method the Generation II games use for calculating whether a Pokémon is Shiny or not, an Egg bred from an alternately-colored Pokémon has a chance as high as 1/64 of being alternately colored itself, but only if the offspring is of the opposite gender as the Shiny parent. This does not apply in later games, however.
In Generation III, a bred Pokémon has the same chance of being Shiny as any Pokémon met in the wild.
In Generation IV, a new mechanic was added to breeding: there is now a five fold increased chance (5/8192 or 1/1639 as opposed to the regular chance of 1/8192) of hatching a Shiny Pokémon when both parents are from different language games. This is due to special coding written into the game by director Junichi Masuda. Aside from this addition, the means of breeding for Shininess are otherwise unchanged.
In Generation V, the odds of the Masuda method's success rate increased from 5/8192 (1/1639) to 6/8192 (1/1366).
In the anime
In the anime, Pokémon breeding refers to an entire line of work practiced by Pokémon Breeders, such as Brock. So far, the anime has shown and discussed little about the literal breeding of Pokémon to produce Eggs, but it is assumed this is part of a Pokémon Breeder's work. It has been shown that Professors get their starter Pokémon from breeders who specifically raise and breed them, like Old Man Swamp from A Mudkip Mission. There are also a few farm-like facilities that produce Pokémon Eggs of various species. Ash received his Eggs from such locations, as did May and her Egg.
Pokémon breeding in the anime focuses heavily on raising healthy Pokémon and keeping them in top condition by grooming them well and feeding them nutritious food.
- Some aspects of breeding in the games have spawned debate and confusion, in particular, Pokémon which breed differently depending on whether they hold an incense item. However, the necessity for an item that wasn't available in previous generations explains why the resulting baby Pokémon wasn't available either.
- Some unusual pairings of Pokémon can be found within the Egg groups, such as Seviper and Zangoose (which are even said to be mortal enemies), and the most famous pairing: Skitty and Wailord. Indeed, the characters in the game make special mention of the fact that no one has seen Pokémon breed.
- One particularly unusual oddity is that Nidorina and Nidoqueen cannot breed, despite the fact that their pre-evolution and male counterparts can.
- Although there is no known way for legendary Pokémon to be bred, there is evidence that it can occur somehow, since Eggs with Articuno, Zapdos and Moltres can be hatched in Pokémon Snap and a baby Lugia has been seen in the anime. Likewise, Manaphy can be hatched from a special Egg from Pokémon Ranger in Pokémon Diamond and Pearl. Furthermore, Manaphy is the only legendary Pokémon who can breed with a Ditto. However, the offspring will always be Phione, who doesn't evolve into Manaphy.
- When a Pokémon hatches from an Egg during both Generation II and Generation III, it is at level 5. However, many Pokémon from the wild can be found between levels 2 and 4, which is below the level of newly hatched Pokémon. This oddity had since been addressed in Generation IV, where all hatched Pokémon started at level 1.
- Despite conventional wisdom, no negative effects occur from inbreeding Pokémon in Generation III onward. Conversely in Generation II, it is not possible for related Pokémon to produce any Egg with one another, despite related animals in real life still being able to produce offspring despite their genetic relationship; this was simply due to the manner of which individual values were stored in the Generation II game's data structure.
- The Pokémon Mansion journals (which predate Generation II's introduction of breeding) describe Mew giving birth as opposed to laying an Egg. These were not retconned in Pokémon FireRed and LeafGreen.