From type/Dateish

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multi method later(DateTime:D: *%unit)

Returns an object based on the current one (belonging to any class that mixes this role in), but with a time delta applied. The time delta can be passed as a named argument where the argument name is the unit.

Unless the given unit is second or seconds, the given value will be converted to an Int.

Allowed units are second, seconds, minute, minutes, hour, hours, day, days, week, weeks, month, months, year, years. Please note that the plural forms can only be used with the later and earlier methods.

The :2nd form of colonpairs can be used as a compact and self-documenting way of specifying the delta:

say DateTime.new('2015-12-24T12:23:00Z').later(:2years);
# OUTPUT: «2017-12-24T12:23:00Z␤»

Since addition of several different time units is not commutative, only one unit may be passed (and the first multi will be used).

my $d = DateTime.new(date => Date.new('2015-02-27'));
say $d.later(month => 1).later(:2days);  # OUTPUT: «2015-03-29T00:00:00Z␤» 
say $d.later(days => 2).later(:1month);  # OUTPUT: «2015-04-01T00:00:00Z␤» 
say $d.later(days => 2).later(:month);   # same, as +True === 1

You can also (since release 2021.02 of the Rakudo compiler) pass several units at the same time, but you will have to join them in a List to activate the second form:

say DateTime.new(date => Date.new('2015-02-27')).later( (:1month, :2days) )
# OUTPUT: «2015-03-29T00:00:00Z␤» 

If the resultant time has value 60 for seconds, yet no leap second actually exists for that time, seconds will be set to 59:

say DateTime.new('2008-12-31T23:59:60Z').later: :1day;
# OUTPUT: «2009-01-01T23:59:59Z␤»

Negative offsets are allowed, though earlier is more idiomatic for that.

Objects of type Date will behave in the same way:

my $d = Date.new('2015-02-27');
say $d.later(month => 1).later(:2days);  # OUTPUT: «2015-03-29␤» 
say $d.later(days => 2).later(:1month);  # OUTPUT: «2015-04-01␤» 
say $d.later(days => 2).later(:month);   # same, as +True === 1