You could try Date::Calc. From its docs:

8) How can I add a week offset to a business date (including across year boundaries)?

             use Date::Calc qw( Business_to_Standard Add_Delta_Days
                                Standard_to_Business );

             @temp = Business_to_Standard($year,$week,$dow);

             @temp = Add_Delta_Days(@temp, $week_offset * 7);

             ($year,$week,$dow) = Standard_to_Business(@temp);
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Phil