One working extra or less is reflected most evidently in the monthly figures on production of goods, for instance in manufacturing industry or energy. Effects of 3 percent for one working day more or less are measured with or without regression analysis. For quarterly figures on economic growth, regression analysis is applied to measure the effects of the number of working days. The effect appears to be less than proportional. Elasticity is in the order of 20 to 25 percent. In the estimates for 2008, the effects of an extra working day are taken into account.