Use your paladin level as druid level
The Divine Bond class ability says:
The second type of bond allows a paladin to gain the service of an unusually intelligent, strong, and loyal steed to serve her in her crusade against evil. This mount is usually a heavy horse (for a Medium paladin) or a pony (for a Small paladin), although more exotic mounts, such as a boar, camel, or dog are also suitable. This mount functions as a druid’s animal companion, using the paladin’s level as her effective druid level
This is a common wording on class and abilities that allow you to have an animal companion, and means you substitute the druid levels on the Animal Companion table by the class levels of the class that grants you the companion.
To figure out the mount stats, simply follow the table, you don't use any of your stats for your companion. For instance, a 5th level paladin's divine bond companion has:
- 5HD, +3 BAB, +4 Fort, +4 Reflex, +1 Will, 5 skill ranks, 3 feats, +2 natural armor bonus, +1 str/dex, 2 bonus tricks, link, share spells, evasion, ability bonus.
Then apply that on the chosen mount stats, given in the companion rules.
The note about the companion's BAB, "is the same as that of a druid of a level equal to the animal’s HD", is actually a simplification. All animal companions follow the bestiary rules, first and foremost, and being creatures of the Animal type, they have a 3/4 BAB (medium) progression.
To make it simpler to new players, and due to the fact that the core book came out before the first bestiary, the book tells us to look at the druid's BAB progression, as that is the same (3/4). The table makes this clear if you actually check the values.
A first level animal companion has 2 HD and +1 BAB, which is the same BAB as a 2nd level druid. If you keep following it down, all numbers will match. The same happens to ability score increases (every 4 HD), skill points (1 per HD) and extra feats (every odd HD) and their saves, follow the table and there won't be any mistake.
Example (Horse)
Let's use a Horse stats as an example and build its stats:
Size Large; Speed 50 ft.; AC +4 natural armor; Attack bite (1d4), 2 hooves* (1d6); Ability Scores Str 16, Dex 13, Con 15, Int 2, Wis 12, Cha 6; Special Qualities low-light vision, scent.
Applying a 5th effective druid level bonuses, apply the ability bonus gained to strength, and replacing its intelligent to 6 (as noted under Divine Bond) we get:
Size Large; Speed 50 ft.;
AC +6 natural armor, +2 Dex, -1 size. Total AC 16;
Attack bite (1d4), 2 hooves* (1d6);
Ability Scores Str 18, Dex 14, Con 15, Int 6, Wis 12, Cha 6;
Saving Throws Fort +6, Reflex +6, Will +2
Special Qualities low-light vision, scent.
Now, we calculate its attack using the increased strength and the BAB as noted on the table:
- Bite: +6 attack bonus (+3 BAB, +4 Str, -1 size), 1d4+4 damage;
- Hooves: +6 attack bonus, 1d6+4 damage;
Note that Hooves are secondary natural attacks, and as such, they take a -5 penalty on the attack bonus and use only 1/2 your strength bonus on damage, as noted under the Natural Attacks universal monster ability. So we adjust the attack accordingly:
- Bite: +6 attack bonus 1d4+4 damage;
- Hooves: +1 attack bonus (+3 BAB, +4 Str, -1 size, -5 secondary), 1d6+2 damage;
