Lost Time Injury Severity Rate (LTISR) Calculator

What is Lost Time Injury Severity Rate (LTISR)?

Lost Time Injury Severity Rate (LTISR) is a workplace safety KPI that measures the severity of lost time injuries by quantifying lost workdays relative to total exposure hours worked.

LTISR answers a different question than LTIFR:

  • LTIFR tells you how often lost time injuries happen.
  • LTISR tells you how severe those injuries are (in terms of days lost).

Organizations use LTISR to understand whether injuries are resulting in longer absences, prolonged recovery, or weak controls in high-risk activities.

LTISR Formula

The general formula to calculate LTISR is:

LTISR = (Total Lost Workdays × Multiplier) ÷ Manhours Worked

Where:

  • Total Lost Workdays = number of workdays lost due to lost time injuries during the reporting period
  • Manhours Worked = total hours worked during the reporting period (employees + contractors as per your scope)
  • Multiplier = 1,000,000 (common global) or 200,000 (OSHA style) or 100,000 (smaller sites/projects)

Why do we use 1,000,000 or 200,000 or 100,000?

  • 1,000,000 hours is widely used internationally and produces stable benchmarking numbers.
  • 200,000 hours is commonly used in OSHA-style reporting (approx. 100 workers × 40 hrs/week × 50 weeks).
  • 100,000 hours is sometimes used for smaller sites/projects to avoid very small decimals.

Important: Do not compare LTISR values calculated using different multipliers unless you standardize the multiplier.

Important Notes (Before You Calculate)

  • Count lost days consistently: Define whether you use calendar days or scheduled working days and keep it consistent across months.
  • Delayed time loss: If an injury becomes a lost time case later, record the lost days in the period when the absence occurs (as per your internal rule).
  • Intermittent absence: If the same injury causes intermittent absences, track total days lost for that case as per your procedure (avoid double counting cases).
  • Scope matters: If you include contractor injuries, include contractor manhours too (for correct exposure).

LTISR Calculator – Quick & Easy

Use the calculator below to compute LTISR instantly:

Result:

Your result will appear here

Tip: LTISR should be reviewed together with LTIFR. Low frequency with high severity may indicate major injury events.

Worked Example: How to Calculate LTISR

Assume during the month:

  • Total Lost Workdays = 60
  • Total Manhours Worked = 2,400,000
  • Multiplier = 1,000,000
LTISR = (60 × 1,000,000) ÷ 2,400,000
LTISR = 60,000,000 ÷ 2,400,000
LTISR = 25.00

Result: LTISR is 25.00 lost days per 1,000,000 man-hours.

Why Tracking LTISR is Important?

  • Measures injury impact: Shows how severe your LTI outcomes are (lost days), not only how often injuries happen.
  • Improves prevention focus: High LTISR indicates serious harm or high-consequence events—focus on critical risk controls.
  • Supports ISO 45001 management review: Helps evaluate effectiveness of controls and safety objectives over time.
  • Better benchmarking: Two sites can have the same LTIFR but different LTISR, meaning different injury severity performance.

How to Reduce LTISR

  • Prioritize critical risk controls for high-severity hazards (working at height, vehicle movement, electrical, confined space, lifting).
  • Improve supervision and permit-to-work compliance for high-risk activities.
  • Strengthen pre-task risk assessments (JSA/TRA) and verify control effectiveness on-site.
  • Implement competency-based training for critical tasks (operators, supervisors, contractors).
  • Conduct high-quality incident investigations and implement permanent corrective actions, not temporary fixes.

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LTISR FAQ

1) What is the difference between LTIFR and LTISR?
LTIFR measures frequency (number of lost time injuries). LTISR measures severity (lost workdays due to lost time injuries).

2) Should we count calendar days or working days?
Use whichever your organization defines, but keep it consistent across months/years and document the rule.

3) Can LTISR be high even when LTIFR is low?
Yes. One serious injury with long absence can significantly increase LTISR even if only one LTI occurred.

4) Which multiplier should we use?
Use the multiplier specified by your corporate standard or regulator (often 1,000,000 globally or 200,000 in OSHA-style reporting). Consistency is key for benchmarking.

Standards & Reference Notes (Commonly Used)

  • ISO 45001 (Occupational health and safety management systems) – requires organizations to monitor and evaluate OH&S performance using appropriate indicators.
  • OSHA Recordkeeping (29 CFR 1904) – widely referenced for injury classification in OSHA-style KPI reporting (especially 200,000 multiplier usage in some practices).
  • ILO guidance on OSH performance – encourages use of lagging and leading indicators for performance evaluation.
  • Legacy industry benchmarking practices – many organizations align with long-standing frequency/severity rate methodologies for comparability across sites.

Conclusion

Lost Time Injury Severity Rate (LTISR) is a key safety KPI used to measure the severity of workplace injuries through lost workdays. Use the LTISR calculator above to compute severity consistently and support HSE dashboards, audits, and management review decisions.

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