A WELLBY, or Wellbeing-Year, is a method for measuring the effectiveness of wellbeing interventions. The WELLBY is used by HM Treasury in the UK and by the New Zealand Treasury to put a financial value on how wellbeing interventions affect people's lives and contribute to social value. WELLBYs can also reveal benefits that traditional measures might miss.

One WELLBY is equivalent to a one-point increase in wellbeing on a measured scale, for one person, for one year. Often, the scale used is life satisfaction, which is the scale we use to report on at Action for Happiness. 

The image below shows how we calculate our outcomes and cost-effectiveness using WELLBYs. 

The WELLBY system is not perfect, but it is a good indicator and provides a baseline for comparing the work of different programs, interventions and organisations. WELLBYs can tell us if an intervention is good value for money.