According to the national statistics office, SCB, the switch will raise its jobless rate by about 2 percentage points.
The centre-right coalition government decided earlier this year to alter the statistics, which they said had failed to register the real jobless tally and helped previous governments present an overly upbeat picture of the labour market.
The main change is that students actively looking for work will be included in the jobless figures. The unemployment rate, which was 3.9 percent in May, would have been 6.0 percent under the new statistical method, SCB said.
The number of unemployed would have been 290,000 versus the 181,000 reported according to the old method.