- If the Pokémon is the first stage in an evolution line, its base experience is the sum of its base stats multiplied by four, then divided by twenty and rounded to the nearest whole number.

- If the Pokémon is the second stage in an evolution line or a non-legendary standalone, its base experience is the sum of its base stats multiplied by seven, then divided by twenty and rounded to the nearest whole number.

- If the Pokémon is the third stage in an evolution line or a legendary, its base experience is the sum of its base stats multiplied by nine, then divided by twenty and rounded to the nearest whole number.

There are a few exceptions to this rule, usually to compensate for abilities that make the Pokémon overall weaker than its base stat total would indicate. Additionally, the Unova starters also have the lowest experience yield of any Pokémon, presumably so you won't have your starter gaining multiple levels before you get out of your house, Volcarona is counted as if it were a legendary rather than a second stage (but Larvesta is counted as a first stage as expected), and Audino and the Chansey family have much higher base experience values than they ought to because giving inordinate amounts of experience is kind of their thing (they have about 2.5 times the base experience they should). However, unless your Pokémon has a crippling ability, you can just use the formula as given above and you'll have your base experience. And if it does have a crippling ability, just find a Pokémon that you'd estimate to be roughly as powerful as yours is after adjusting for the ability and use its base stat total or something close to it in the formula instead.