Leading researcher Sonya Lyubomirsky has been able to determine that about 40 percent of our capability for happiness is underdeveloped and within our power and ability to change. About 10 percent can be attributed to life circumstances and 50 percent of our happiness is set.

Lyubomirsky developed an assessment of personal happiness through a brief 4-item scale called The Subjective Happiness Scale. It assigns you to an activity that helps to bring a little more joy into your life.

Source: https://psychcentral.com/