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 $4.88 million. The US average reaches $10.22 million. Healthcare breaches average $10.93 million globally and remain the most expensive vertical for the fourteenth consecutive year. Financial services average $5.97 million. The average rises 10 percent year-over-year, driven by ransomware demands, longer dwell times, and regulatory penalties. Detection within 200 days reduces total breach cost by approximately $1 million versus longer dwell times.

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 report finds that organisations with mature security analytics (typically including SIEM) detect breaches in 73 days on average against 207 days for organisations without. Time-to-respond drops from 73 days to 29 days. The mechanism: SIEM correlates events across log sources to surface attack chains earlier, automates initial triage to free analyst time, and provides forensic context that accelerates investigation. The dollar value of those reductions, applied to typical breach cost, often exceeds annual SIEM TCO by 3-5x.

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.