PurposeThere is ongoing debate amongst in-work poverty researchers as to how to answer the question “who is counted as in-work poor?” and how to define the minimum size of work that should be used to determine a “working threshold”. The purpose of this paper aims to contribute to this debate by testing five different definitions of a “working threshold” and discussing their implications when testing the different measurement outcomes.Design/methodology/approachThe authors use data from Statistics Sweden (SCB), including the total population registered as living in Sweden for each year from 1987 to 2017. All calculations are on a yearly basis and in fixed prices (2017). The data set used is based on linked administrative data retrieved from Statistics Sweden and the software used is SAS 9.4.FindingsResults show how in-work poverty trends differ by measurement approach. The two definitions with the lowest income thresholds are found to include a very heterogenic group of individuals. The development of in-work poverty in Sweden over 30 years show decreasing in-work poverty during the first decade followed by an increase to almost the same levels at the end of the period. In-work poverty in Sweden has transformed from being female-dominated in 1987 and the typical person in in-work poverty 2017 is a male immigrant, aged 26–55 years.Practical implicationsThis methodological discussion might lead to a new definition of who is a worker amongst the in-work poor, which could consequently affect who is counted as being in in-work poverty and lead to new social policy measures.Originality/valueThis is, to the authors' knowledge, the first time different definitions of work requirement used to define in-work poverty have been tested on a data set including the total population and over a period of 30 years.