SIEM ROI calculator: build the business case for SIEM investment

Use Return on Security Investment (ROSI), not traditional ROI. The formula: ROSI = (monetary risk reduction - SIEM cost) / SIEM cost. Monetary risk reduction equals breach cost (single loss expectancy) multiplied by breach probability multiplied by SIEM's risk reduction percentage. For a typical mid-market organisation with $4.45M average breach cost, 28 percent annualised breach probability, 35 percent SIEM risk reduction, and $280K SIEM cost: monetary risk reduction is $436K, ROSI is 56 percent, payback period is 7.7 months. The interactive calculator on this page lets you model your specific inputs.

The IBM Cost of a Data Breach Report 2025 puts the global average at $4.44 million, down 9 percent year-over-year as faster AI-assisted containment pulled costs down for the first time in five years. The US average moved the other way, hitting a record $10.22 million, up 9 percent, on higher regulatory and detection costs. Healthcare breaches average $7.42 million and remain the most expensive vertical for the fourteenth consecutive year. Financial services average $5.56 million. The global mean time to identify and contain a breach fell to 241 days, the lowest in nine years.

SIEM rarely justifies itself for organisations under 50 employees with no compliance requirements, no sensitive data, and no regulatory obligations. For those organisations, basic EDR plus cloud-native logging is usually sufficient. SIEM also rarely justifies itself for organisations where MDR or XDR provides equivalent detection at lower cost: roughly 100-1,000 employees with cloud-native infrastructure and limited compliance scope. Above 1,000 employees or with PCI, HIPAA, SOX, or SOC 2 compliance, SIEM is effectively non-negotiable.

IBM's 2025 report puts the global mean time to identify and contain a breach at 241 days (158 to identify, 83 to contain), the lowest in nine years. Organisations using AI and automation extensively across security operations cut that lifecycle by about 80 days and held average breach cost to $3.62 million against $5.52 million for non-users, a $1.9 million gap. SIEM is the correlation layer those programmes are built on: it surfaces attack chains across log sources earlier, automates initial triage to free analyst time, and provides forensic context that accelerates investigation. The dollar value of a faster lifecycle, applied to typical breach cost, often exceeds annual SIEM TCO by several times.

Five quantifiable secondary benefits: compliance audit cost reduction (30-60 percent shorter audits with structured SIEM evidence, $50K-$200K saved per year), cyber insurance premium reduction (10-25 percent typical), analyst productivity gains (30-50 percent reduction in tier-1 alert volume via correlation), mean time to recover from non-breach incidents (40-60 percent faster), and reputational protection (qualitative but real). Layer these on top of the breach-prevention ROSI for the full picture.