From type/Date

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method new-from-daycount($daycount,:&formatter --> Date:D)

Creates a new Date object given $daycount which is the number of days from epoch Nov. 17, 1858, i.e. the Modified Julian Day. Optionally accepts a formatter as a named parameter.

say Date.new-from-daycount(49987);          # OUTPUT: «1995-09-27␤»