Call of Cthulhu 7e: Dice & Strategy Guide

Call of Cthulhu, now in its 7th edition, is the great horror-investigation roleplaying game. Its dice system is refreshingly simple — a single percentile roll settles almost everything — but the game rewards a mindset most RPGs don’t: caution, curiosity and knowing when not to roll at all.

What dice CoC uses

The star is percentile dice (d100), rolled as two ten-sided dice — one read as the “tens” and one as the “units” — to produce a result from 1 to 100 (00 on both dice reads as 100). A few other dice appear for damage and characteristics (d4, d6, d8, and combinations like 1d10 or 2d6+6), but the resolution engine is pure percentile.

The core mechanic is roll-under: your skills and characteristics are percentage values, and you succeed by rolling equal to or under the relevant number. If your Library Use is 60, you want a d100 result of 60 or less. This means a higher skill is better and the number on your sheet is your chance of success — wonderfully intuitive.

Success, failure and levels of success

A roll isn’t just pass or fail; 7th edition grades how well you did against thresholds derived from your skill value:

• Regular success — roll at or under your full skill value.
• Hard success — roll at or under half your skill.
• Extreme success — roll at or under one-fifth of your skill.
• Critical — a roll of 01.
• Fumble — a very high roll (typically 96–100, or 100 for higher-skilled characters) that goes badly wrong.

Opposed rolls and tougher tasks call for a hard or extreme success, so a high skill both succeeds more often and reaches those better tiers more reliably.

Bonus and penalty dice

Instead of flat modifiers, CoC 7e adjusts the odds with extra tens dice. When conditions favour you, roll a bonus die: an additional tens die, and you keep the lower tens result. When conditions hinder you, roll a penalty die and keep the higher tens result. Multiple bonus and penalty dice cancel one another out. Because they shift the tens digit, a bonus die is a large, tangible swing in your favour — and worth seeking out through good positioning and preparation.

How a roll (and a turn) plays out

Most of the game is freeform investigation: you describe what your investigator does, and the Keeper calls for a roll only when the outcome is uncertain and matters. You roll d100, compare to your skill, and read the level of success. If you fail an important, non-combat roll you may be able to push it — try again by committing harder, accepting that a second failure brings a worse, Keeper-decided consequence than the first. Combat runs in rounds by DEX order, with attacks resolved as opposed rolls and dangerous foes able to end an investigator in a single exchange.

Sanity

Sanity (SAN) is the resource that defines the game. Witnessing horrors forces a Sanity roll (roll under your current SAN); failure costs Sanity points, and large single losses can trigger bouts of madness. Encountering the Mythos is meant to be costly — managing that erosion, not avoiding it entirely, is the real game.

Winning and effective strategy

• Avoid combat. Investigators are fragile and firearms are lethal. A fight you can talk, sneak or run your way out of is almost always the better outcome. Treat violence as a last resort, not a plan.
• Investigate thoroughly. The game is solved with information. Spread skills across the group, follow leads, and remember that in 7e a plain success on a core clue-finding roll should reveal the essential clue — you dig for the extra, not the basic lead.
• Manage your Sanity. Ration your exposure. Don’t stare at the unspeakable when a glance will do, lean on the reassurance of allies, and let higher-SAN characters take the worst sights when you can choose.
• Don’t push dangerous rolls. Pushing is powerful for a locked door or a stubborn book, but never push a roll where a second failure could get someone killed — the consequence is meant to escalate.
• Prepare to earn bonus dice. Scouting, the right tool, extra time and teamwork can all justify a bonus die. Engineering good conditions beforehand beats gambling on a straight roll.

Beginner tips and common mistakes

• Remember you want low. Roll-under trips up players used to d20 systems — a low number is a good number here.
• Don’t treat it like D&D. Kicking down doors and charging monsters gets investigators killed. Curiosity and caution are your best abilities.
• Spread the skills. A party that covers Spot Hidden, Library Use, Persuade, Medicine and Occult between them will crack a scenario one investigator never could.
• Expect loss. Losing Sanity, and sometimes characters, is part of the horror. Play into it rather than fighting to keep everyone pristine.
• Ask before you roll. Often you don’t need dice at all — good questions and roleplay uncover more than a fistful of failed checks.

Curious about another dice-pool horror game? Read our Vampire: The Masquerade dice & strategy guide.