$daysfrom = ($yyyy % 4 ? 365 : 366) isn't sufficient for leap years .. there's another part of the rule -- e.g. Feb 1900 only had 28 days but Feb 2000 had 29. google results

I see you were trying to avoid other modules, but just for an example (and cause it's a module i use alot), here's a partial Date::Calc solution: 
my $birthday = '2000-01-02'; # yyyy-mm-dd
use Date::Calc qw/Delta_Days Today Add_Delta_YMD/;
my @date = split /-/, $birthday;
$date[0] = (Today())[0];  # set the year to current year
print Delta_Days( Add_Delta_YMD(@date,-1,0,0), @date );  # days since 
+last one
print Delta_Days( @date,  Add_Delta_YMD(@date,1,0,0) );  # days until 
+next one

[download]
Update: added in the Add_Delta_YMD to account for birthdays on 2/29

In reply to Re: Calculate Age, days to next and days from last for a given birthday by davidrw
in thread Calculate Age, days to next and days from last for a given birthday by ruzam

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