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QALY (Quality-Adjusted Life Year)

Calculate QALYs and cost-effectiveness for health interventions. Enter values for instant results with step-by-step formulas.

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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.

Background & Theory

The Quality-Adjusted Life Year (QALY) Estimator applies the following established principles and formulas. Break-even analysis identifies the sales volume at which total revenue equals total costs, producing neither profit nor loss. The formula divides total fixed costs by the contribution margin per unit, where contribution margin equals selling price minus variable cost per unit. If a software product has $50,000 in monthly fixed costs and each licence generates $20 above its variable cost, break-even requires 2,500 unit sales per month. Above that threshold, each additional unit contributes directly to profit. Gross margin expresses the percentage of revenue remaining after direct cost of goods sold: gross margin equals revenue minus COGS, divided by revenue. A SaaS company with 80 percent gross margins retains $0.80 of every revenue dollar to cover operating expenses, while a manufacturer with 30 percent gross margins faces much tighter operating leverage. Customer acquisition cost (CAC) divides total sales and marketing expenditure in a period by the number of new customers acquired in that same period. Customer lifetime value (LTV) estimates the total profit attributable to a customer relationship. The standard formula multiplies average revenue per user (ARPU) by gross margin and divides by the monthly churn rate. A business with $50 ARPU, 75 percent gross margin, and 2 percent monthly churn has an LTV of $1,875. The LTV:CAC ratio benchmarks unit economics health; a ratio above 3:1 is generally considered sustainable, while ratios below 1:1 indicate the business is acquiring customers at a loss. Burn rate measures monthly cash expenditure net of revenue. Cash runway equals current cash reserves divided by net monthly burn. A company with $1.2 million in the bank burning $100,000 per month has twelve months of runway. The Rule of 40 is a benchmark for SaaS health: the sum of annual revenue growth rate (as a percentage) and profit margin (as a percentage) should equal or exceed 40. High-growth companies burning cash can still pass this rule if their growth rate compensates.

History

The history behind the Quality-Adjusted Life Year (QALY) Estimator traces back through the following developments. Early economic thought centred on mercantilism, the 16th and 17th century doctrine that national wealth derived from accumulating precious metals through export surpluses and colonial extraction. Adam Smith's "Wealth of Nations" in 1776 dismantled this framework, arguing that genuine prosperity arose from specialisation, division of labour, and freely operating markets. David Ricardo extended Smith's work with the theory of comparative advantage in 1817, demonstrating mathematically that mutually beneficial trade was possible even when one country was less productive in every industry. Alfred Marshall's "Principles of Economics" published in 1890 provided the modern framework of supply and demand curves, consumer surplus, price elasticity, and marginal analysis, establishing neoclassical economics as the dominant academic paradigm for decades. The Great Depression exposed the limits of laissez-faire assumptions, and John Maynard Keynes's "General Theory of Employment, Interest and Money" in 1936 argued that private-sector aggregate demand failures required countercyclical government fiscal intervention to restore full employment, shifting the policy consensus toward active macroeconomic management. The post-World War II decades constructed mixed-economy models combining market allocation with expanded welfare states and Keynesian demand management. Milton Friedman and the Chicago School challenged this consensus from the 1960s onward, championing monetarism and arguing that stable money supply growth was superior to discretionary fiscal policy. Their influence shaped the deregulatory and privatisation policies of the Reagan and Thatcher eras in the 1980s. Behavioural economics emerged through the work of Daniel Kahneman and Amos Tversky in the 1970s and Richard Thaler in the 1980s, using psychology to demonstrate that real human decision-making deviates systematically from rational-actor models through heuristics and biases. The rise of the internet and mobile platforms in the 2000s and 2010s created a new category of platform economics, where network effects, near-zero marginal cost of digital goods, and two-sided market dynamics generated winner-take-most competitive outcomes requiring new analytical frameworks for business valuation.

References