QALY (Quality-Adjusted Life Year)
Calculate QALYs and cost-effectiveness for health interventions. Enter values for instant results with step-by-step formulas.
Formula
QALY = Years × Quality; Cost/QALY = Cost / QALYs Gained
Worked Examples
Example 1: Joint Replacement Surgery
Problem: 65-year-old with arthritis. Current quality: 0.6 (moderate pain/mobility issues). Life expectancy: 20 years. Hip replacement costs $40,000, expected to improve quality to 0.85 for 15 years.
Solution: Baseline (no surgery):\nQALY = 20 years × 0.6 quality = 12.0 QALYs\n\nWith hip replacement:\nYears 1-15: 0.85 quality\nYears 16-20: 0.6 quality (assumed decline)\n\nQALY = (15 × 0.85) + (5 × 0.6)\nQALY = 12.75 + 3.0 = 15.75 QALYs\n\nQALY gained: 15.75 - 12.0 = 3.75 QALYs\n\nCost per QALY:\n$40,000 / 3.75 = $10,667 per QALY\n\nAssessment:\nWell below $50,000 threshold\nVery cost-effective intervention\nClear recommendation for coverage
Result: 3.75 QALYs gained | $10,667 per QALY | Very cost-effective
Example 2: Expensive Cancer Drug
Problem: Stage 4 cancer patient. Current quality: 0.4 (significant symptoms). Life expectancy without treatment: 1 year. New drug costs $200,000, extends life 8 months at quality 0.5.
Solution: Baseline (no drug):\nQALY = 1 year × 0.4 quality = 0.4 QALYs\n\nWith drug:\nTotal time: 1 year + 8 months = 1.67 years\nAssume quality 0.5 for extended period, 0.4 for original expectancy\n\nQALY = (1 × 0.4) + (0.67 × 0.5)\nQALY = 0.4 + 0.33 = 0.73 QALYs\n\nQALY gained: 0.73 - 0.4 = 0.33 QALYs\n\nCost per QALY:\n$200,000 / 0.33 = $606,060 per QALY\n\nAssessment:\nFar exceeds $150,000 threshold\nNot cost-effective by standard metrics\nMay still be approved under end-of-life exceptions or patient advocacy
Result: 0.33 QALYs gained | $606,060 per QALY | Not cost-effective by standard thresholds
Example 3: Preventive Intervention
Problem: Lifestyle program for diabetes prevention. Costs $5,000. Reduces diabetes risk by 50% over 10 years. Without intervention: 30% chance of diabetes (quality drops from 0.9 to 0.7). 25 years remaining life expectancy.
Solution: Baseline (no intervention):\n70% chance: healthy = 25 × 0.9 = 22.5 QALYs\n30% chance: diabetes at year 5 = (5 × 0.9) + (20 × 0.7) = 18.5 QALYs\nExpected: 0.7 × 22.5 + 0.3 × 18.5 = 15.75 + 5.55 = 21.3 QALYs\n\nWith intervention (50% risk reduction → 15% chance):\n85% healthy: 22.5 QALYs\n15% diabetes: 18.5 QALYs\nExpected: 0.85 × 22.5 + 0.15 × 18.5 = 19.125 + 2.775 = 21.9 QALYs\n\nQALY gained: 21.9 - 21.3 = 0.6 QALYs\n\nCost per QALY:\n$5,000 / 0.6 = $8,333 per QALY\n\nAssessment:\nHighly cost-effective prevention\nEven better if population-level
Result: 0.6 QALYs gained | $8,333 per QALY | Highly cost-effective prevention
Frequently Asked Questions
What is a QALY?
Quality-Adjusted Life Year (QALY) combines quantity and quality of life into a single metric. 1 QALY = 1 year lived in perfect health. 0.5 QALY = 1 year at 50% quality OR 6 months at perfect health. Used to compare health interventions that affect both lifespan and quality of life.
How is quality of life measured for QALY?
Quality weights (0-1) come from standardized surveys: EQ-5D (mobility, self-care, activities, pain, anxiety), SF-6D, or HUI. Weights are derived from population preferences—how much of lifespan people would trade for better quality. 1.0 = perfect health, 0 = death, negative values = states worse than death.
What's a cost-effective QALY threshold?
Common thresholds: US typically $50,000-150,000 per QALY, UK's NICE uses £20,000-30,000 (~$25,000-38,000). These aren't absolute—orphan diseases, end-of-life care, and severity may justify higher costs. Below threshold = recommended, above = may still be approved with justification.
What are QALY limitations?
Limitations: 1) Assumes quality can be quantified, 2) May undervalue elderly (fewer years to gain), 3) Weights come from general public, not patients, 4) Doesn't capture non-health value (work, family), 5) Controversial for severe disabilities (some see as discriminatory). DALYs are alternative metric.
What's the difference between QALY and DALY?
QALY measures health gained (more is better). DALY (Disability-Adjusted Life Year) measures health lost (fewer is better). DALYs = Years of Life Lost + Years Lived with Disability. WHO uses DALYs for global burden of disease. Both serve similar purposes with opposite framing.
How do you estimate quality weights?
Methods: 1) Standard Gamble—choose between certain health state vs gamble on perfect health/death, 2) Time Trade-Off—years in poor health you'd trade for fewer in perfect health, 3) EQ-5D survey—standardized questionnaire mapped to weights. Clinical trials often use EQ-5D.