Interactive Probability Calculator
Adjust the sliders below to see how different combinations of dice pool, skill bonus, and target number affect your success chances. The kept dice slider demonstrates the Keep strategy.
Interactive Probability Calculator
Results
Dice Pool Statistics
Understanding the statistical properties of different dice pool sizes helps you make informed decisions about character builds and Imagination Point spending.
| Pool | Average | Min | Max (no exp) | Max (with exp) | Std Dev |
|---|---|---|---|---|---|
| 1d6 | 4.2 | 1 | 6 | 12 | ±1.7 |
| 2d6 | 8.3 | 2 | 12 | 24 | ±2.4 |
| 3d6 | 12.5 | 3 | 18 | 36 | ±3 |
| 4d6 | 16.7 | 4 | 24 | 48 | ±3.4 |
| 5d6 | 20.9 | 5 | 30 | 60 | ±3.8 |
| 6d6 | 25 | 6 | 36 | 72 | ±4.2 |
| 7d6 | 29.2 | 7 | 42 | 84 | ±4.5 |
| 8d6 | 33.4 | 8 | 48 | 96 | ±4.8 |
Success Rates by Pool Size
This chart shows how success probability changes with dice pool size. The example uses an Unskilled (+0) character against a Standard difficulty (TN 18).
Key Insight: Pool Size Matters
Moving from 2d6 to 4d6 can double your success rate. Prioritize building dice pools through attributes and help.
Key Insight: Great Success Rarity
Great Success (+8 or more) requires larger pools or high skill. With 3d6+0 vs TN 18, Great Success is only about 15%.
Outcome Tier Distribution
This pie chart shows the probability distribution across all outcome tiers for a typical roll: 4d6 pool, Intermediate skill (+3), vs Standard difficulty (TN 18).
Critical Results
Critical Success (all 6s) and Critical Failure (all 1s) are rare but dramatic. With 4d6, each has only ~0.08% chance.
Partial Success Zone
The Partial Success band (-1 to -4 margin) creates interesting narrative moments - you achieve your goal but with complications.
Skill Tier Impact
This chart shows how skill tier affects success probability with a fixed pool size (4d6) and Standard difficulty (TN 18).
Danger Zone
Incapable (-5) and Deficient (-3) skills make standard tests very difficult. Avoid these situations or find ways to add dice.
Competent Zone
Novice (+1) to Intermediate (+3) represents everyday competence. You'll succeed at standard tasks more often than not.
Mastery Zone
Expert (+7) and Master (+10) skills make even hard tasks manageable. Focus on maximizing one or two key skills.
Imagination Point Impact
Imagination Points (IP) allow you to boost rolls. Here's how different IP expenditures affect a 3d6 pool with +0 skill vs TN 18:
| Option | Effect | Base % | New % | Change | Best For |
|---|---|---|---|---|---|
| 1 IP: +1 die | Add 1d6 to pool | 15.1% | 38.5% | +23.3% | Low attribute characters |
| 1 IP: Upgrade die | d6 → d8 (~+1 avg) | 15.1% | 19.8% | +4.6% | High success tiers |
| 2 IP: Help w/o action | +1 die to ally, keep turn | 15.1% | 38.5% | +23.3% | Critical ally rolls |
Pro Tip: Helping Without Action
Spending 2 IP to help an ally without using your action is expensive but preserves your own turn. Use it when an ally's success is critical and you also need to act.
Keep Strategy Analysis
In DROP, you can choose to 'keep' dice at a fixed value of 4 instead of rolling them. This reduces variance but caps potential. Use the interactive calculator above to explore different keep strategies.
When to Keep
- You're close to the target and need consistency
- You have a large pool and just need to hit the TN
- Failure would be catastrophic
When to Roll All
- You need a Great Success for the bonus effects
- You're significantly below the TN and need explosions
- Partial success is acceptable
Reach & Push Risk Analysis
The Reach and Push mechanics let you attempt actions beyond your normal capability at increasing risk.
Reach
Add +1d6 but upgrade Failure to Critical Failure if you fail.
✓ Worth it when you would fail anyway
✗ Risky if you're borderline
Push (After Failure)
Reroll failed test, but Failure becomes Critical Failure and Critical Failure causes character death.
✓ Last resort for critical situations
✗ Never push casually
⚠️ DROP System v2 Probability Updates
The following sections cover probability analysis for new v2 mechanics.
Zero Dice Probability Analysis
Characters with 0 in an attribute face critical decisions. Here's how the two Zero Dice options compare:
| Option | Expected Value | Success vs TN 12 | Risk |
|---|---|---|---|
| 2d6 Take Lowest | ~2.53 | 0% | Safe (no State) |
| Reach for State | ~4.17 (with explosion) | 0% | Guaranteed State |
When to Take Lowest
Use when you can't afford a State, or when the TN is so high that even the Reach die won't help. Safe failure is better than dangerous failure.
When to Reach for State
Use when you desperately need success and have no other options. The State is guaranteed, but the extra ~1.6 average value could make the difference.
Sets: Probability by Pool Size
The probability of rolling matching dice (Sets) increases significantly with pool size. Here's how likely you are to roll at least doubles:
| Pool | Any Doubles | Any Triples | Expected Bonus |
|---|---|---|---|
| 2d6 | 16.7% | - | +0.17 dice |
| 3d6 | 44.4% | 2.8% | +0.50 dice |
| 4d6 | 72.2% | 9.7% | +0.82 dice |
| 5d6 | 90.7% | 19.4% | +1.11 dice |
| 6d6 | 98.5% | 31.9% | +1.38 dice |
Reach/Push Exclusivity: Strategic Analysis
In v2, once you Push you can no longer Reach until you rest. This creates a critical decision point that affects all future rolls in the session.
Reach-First Strategy
- ✓ Reach early when stakes are lower
- ✓ Build up Reach debt you can recover via Sets
- ✓ Save Push for critical moment
- ⚠️ Risk: accumulating Wound risk from 1s
Conservative Strategy
- ✓ Avoid both until necessary
- ✓ Use Sets to build dice organically
- ✓ Push only as last resort
- ⚠️ Risk: may fail winnable rolls
Single Explosion: Updated Probabilities
In v2, explosions are limited to once per die (no chains). This changes expected values:
| Mechanic | v1 Expected | v2 Expected | Change |
|---|---|---|---|
| Single d6 | 4.20 | 4.17 | -0.03 |
| Max single die | ∞ (theoretical) | 12 | Bounded |
| Explosion 1 = Fail? | Yes | No | Safer |
v2 Explosion Benefits
Rolling a 1 on an explosion die has no negative effects in v2. This makes explosions purely beneficial—there's never a downside to a die exploding.
Strategic Takeaways
For Players
- Build dice pools through attribute investment and teamwork (Help action adds +1d6)
- Specialize skills to Intermediate (+3) or higher for reliable success
- Save Imagination Points for critical rolls; don't spend on routine tests
- Use the Keep strategy when consistency matters more than upside
For Tricksters (GMs)
- Standard TN 18 vs 3d6+3 yields ~65% success - tune difficulty accordingly
- Use graduated difficulty (Easy/Standard/Hard) to create meaningful choices
- Embrace Partial Success as a narrative tool, not a failure
- Remember that State penalties create natural pressure without death spirals