Will the UK's ageing population be vibrant and independent, or suffer from greater chronic ill health? Healthy life expectancy (HLE) is commonly used to try to assess this: it is an estimate of how many years are lived in good health over the lifespan. Such data are invaluable for predicting future needs, evaluating health programmes and identifying trends and inequalities. They can inform planning of health and social services, long term care and pensions. This POSTnote reviews the current debate on HLE, outlines possible future scenarios, and looks at the pros and cons of different HLE measures.