The Happiness Indicator (https://www.happinessindicator.com) is an online tool designed to make people more aware of their own happiness. The theory behind the website is that a keener awareness of one's own happiness helps one find an optimal lifestyle and consequently promotes happiness among users of the website. In this paper, we describe this tool and explore its effectiveness. Users periodically record how happy they feel on the present day and how happy they have felt over the past

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... using the Happiness Comparer. They also have the option of indicating in the Happiness Diary how happy they felt during the various activities of the previous day. Users receive instant feedback in the form of a comparison with their earlier scores and with the average scores of similar users. The website has been online since January 2011; 5411 participants have participated at least twice, and 64% of them used the Happiness Diary one or more times. These numbers are now high enough to permit a first check to see whether repeated use of the Happiness Indicator is followed by the expected rise of the participants' happiness. We found that the use of the Happiness Comparer was followed by a small non-significant increase in happiness, while using the Happiness Diary was followed by a greater increase and statistically significant upturn. Using the Happiness Diary 10 times, was followed by an average increase in happiness of 1,5%. In addition, we found that the relationship between diary use and rise of happiness was particularly strong for those who felt less happy when they first used the Happiness Indicator. 1 Some researchers estimated that about 40% of differences in happiness between people can be explained by how we arrange our lives (e.g. Sheldon and Lyubomirsky 2007). This statistic has been criticized as an overestimation, since it also covers unexplained variance and measurement error. However, there is no doubt that life-choices make a difference, such as in the case of marriage (e.g. Stutzer and Frey 2006) and migration (e.g. Hendriks 2018).