That number will vary much depending on what days of the week various specific dates will occur: 1 Jan, 6 Jan, 1 May, 6 Jun, and 25-26 Dec.

Also, it's important to note that two Swedish red days always fall on Saturdays: Midsummer Day and All Saints' Day. In 2017, there were "only" 8 red days on Mon-Fri, plus two unofficial red days of Midsummer Eve and All Saints' Eve.