Keep in mind, horse breeding doesn't always produce a better horse. It might even be worse or lower Tier than one or both parents. Horse breeding calculators likesomethinglovelywill help you see the chances of obtaining a higher Tier horse.
Input your horse Tier and Level in the calculator and it will show you up to 21 Breeding Chance Levels.
Breeding Chance Level 3 shows a 34% chance of the foal not gaining a Tier. This would be a bad Breeding choice. (T1 Level 1 + T1 Level 1). If you increase just one of the parent horses to Level 2, you would jump up to the next Breeding Chance Level 4. In this case, you are at least guaranteed one increase in Tier.
The numbers with the diagonal colored backgrounds represent each Breeding Chance Level.
As you improve the Level of your parent horses, you will notice the red box move toward the bottom right. If you increase the female parent’s Level by 1, the red box will move down by 1. If you increase the male parent’s level by 1, the red box will move right by 1. The bottom right Breeding Chance Level is the best possible outcome for the two parents you chose. In the image above, the highest possible Breeding Chance Level is 12. That would require both horses being Level 30.
Breeding Chance Levels often include a wide variety of Horse Levels. For example, to reach the next Breeding Level of 5, we could level the horses both to level 5 or do T1 L1 + T1 L10.
Improving a horse's level does not always put your Breeding Chance into the next Tier. Always look ahead to see if it's worth your time to level the parents. In our example, it would do no good to level both horses to level 8, since they would still be in the same Breeding Chance Level of 5. But once they both hit Level 9, it would put them into the next Breeding Tier.
Breeding two Tier 1 parents can result in a Tier 6 foal, but it would take allot of time to level both parents to 30.
The higher you go up in Horse Tiers, the more chance you have of actually getting a lower Tier horse. Breeding two T7 L30 horses still gives a 19% chances of getting a T6 foal. Some of these breed Tiers are just a pain.