Additive Risk Matrix — Score = Probability (0–10) + Impact (0–5) → total 0–15
Impact ↓ / Probability → 0 (Impossible) 1–3 (Very Unlikely) 4–6 (Possible) 7–9 (Likely) 10 (Certain)
0 – No Impact 0
None		 1–3
Low		 4–6
Low		 7–9
High		 10
High
1 – Minor Impact 1
Low		 2–4
Low		 5–7
Medium		 8–10
High		 11
Very High
2 – Moderate Impact 2
Low		 3–5
Medium		 6–8
Medium		 9–11
Very High		 12
Very High
3 – Significant Impact 3
Medium		 4–6
Medium		 7–9
High		 10–12
Very High		 13
Extreme
4 – Major Impact 4
Medium		 5–7
Medium		 8–10
High		 11–13
Very High		 14
Extreme
5 – Severe Impact 5
Medium		 6–8
High		 9–11
Very High		 12–14
Extreme		 15
Extreme
None (0)
Low (1–4)
Medium (5–7)
High (8–10)
Very High (11–13)
Extreme (14–15)
How to use

Calculate Score = Probability (0–10) + Impact (0–5). The total ranges from 0 (none) to 15 (extreme). Use the legend thresholds to prioritize mitigations. For home preparedness, the additive method keeps low-probability but high-impact scenarios visible while also showing common, likely events.

Suggested thresholds (customize to taste):