The Difficulty rating is the skill level at which the bard has a 50% chance of success versus the creature. At this skill level -25.0, the bard has no chance of success and can't make the attempt. At this skill level +25.0, the bard is guaranteed success and cannot gain skill against this creature.

Various modifiers have an effect on the final difficulty. You start with base difficulty and then add or subtract depending on skill levels and instrument used.
- Using an exceptional instrument reduces base difficulty by 5
- Using an aligned "slayer" instrument reduces base diffficulty by 10
- Using an opposite aligned "slayer" instrument increases base difficulty by 10
- If Musicianship skill > 100 then bonus = (Musicianship skill - 100) / 2
- Subtract musicianship bonus from base difficulty
- When provoking, subtract 5 from base difficulty
- When discording or targeted peacemaking, subtract 10 from base difficulty

The % chance of success is 50 + 2 * (Bard Skill - Resulting Difficulty)
Example: At 120.0 skill, a bard with a dragon-slaying instrument has approx. 60% chance of success to use an ability against an Ancient Wyrm, or to provoke two Ancient Wyrms to fight. At 100.0 skill, with the same instrument, the chance is approx. 20%.

There are a few creatures that do not follow the same rules for Bard Difficulty though, those are called "Non-Bardable", which basically means that they are completely immune to all Bard Skill effects, no matter how high your skills are. The list on the right lists all the creatures that are currently known to be "Non-Bardable".

1. Use the Animal Lore skill on the creature
2. Add up the following attributes:
   • Max Hit Points * 1.6
   • Max Stamina
   • Max Mana
   • all Skills
3. Add another 100 points for each of the following abilities:
   • Spell Casting
   • Fire Breath
   • Radiation or Aura Damage (Heat, Cold etc.)
   • Resistance to Poison
   • Lifeforce Draining
4. Add another 20 points for each level of poison attack the creature can do. This ranges from 20 for a level 1 poison attack to 100 for a level 5 poison attack
5. If the creature's stats and skills total is 700 or less, continue with step 7
6. If the creature's stats and skills total is greater than 700, subtract 700 from the end result of step 4, then multiply the result with 0.275, and finally add 700 to that result.
7. Drop the numbers after the decimal point and then divide by 10. The result is the creature's barding difficulty.