Percentile (d100)
Also known as: d100, percentile dice, percent system, BRP · Pronunciation: dee-one-hundred / per-SEN-tile
Definition
A dice mechanic where you roll two d10s as a number from 01-100 and succeed if you roll equal to or under your skill rating. Lower rolls are better.
How it works in different systems
Call of Cthulhu 7e: Roll under skill%. Extreme success = under 1/5 skill. Hard success = under 1/2 skill.
Delta Green: Same as CoC but with different critical thresholds.
WFRP 4e: Roll under skill%. Doubles are criticals (good or bad depending on success).
Mythras: Roll under skill%. Special success at 1/5, critical at 1/20.
Example
“Your investigator has 65% in Library Use. You roll d100 and get 43. Since 43 is under 65, you succeed! If you'd rolled 72, you would have failed.”
Common Mistakes
- Rolling over your skill thinking higher is better (it's not - under is success)
- Confusing which die is tens and which is ones
- Forgetting that 00 + 0 = 100, not 0 (though some tables rule differently)
Origin & History
Popularized by Basic Role-Playing (BRP) system in the 1980s, used in RuneQuest and Call of Cthulhu.