\newcounter{datetoday}
\newcounter{diffyears}
\newcounter{diffmonths}
\newcounter{diffdays}

% Function curtesy of Martin Scharrer
% http://tex.stackexchange.com/questions/14518/difference-between-two-dates
\newcommand{\difftoday}[3]{%
	\setmydatenumber{datetoday}{\the\year}{\the\month}{\the\day}%
	\setmydatenumber{diffdays}{#1}{#2}{#3}%
	\addtocounter{diffdays}{-\thedatetoday}%
	\ifnum\value{diffdays}>0
		\def\diffbefore{in }%
		\def\diffafter{}%
	\else
		\def\diffbefore{}%
		\def\diffafter{}%
		\setcounter{diffdays}{-\value{diffdays}}%
	\fi
	\setcounter{diffyears}{\value{diffdays}/365}%
	\setcounter{diffdays}{\value{diffdays}-365*\value{diffyears}}%
	\setcounter{diffmonths}{\value{diffdays}/30}%
	\setcounter{diffdays}{\value{diffdays}-30*\value{diffmonths}}%
	%
	\diffbefore
	\ifnum\value{diffyears}=0
	\else
		\ifnum\value{diffyears}>1
			\thediffyears\space years\ignorespacesafterend
		\else
			\thediffyears\space year\ignorespacesafterend
		\fi
	\fi
	\ifnum\value{diffmonths}=0
	\else
		\ifnum\value{diffyears}>0
			,
		\fi
		\ifnum\value{diffmonths}>1
			\thediffmonths\space months\ignorespacesafterend
		\else
			\thediffmonths\space month\ignorespacesafterend
		\fi
	\fi
	\diffafter
}

\newcommand{\diffdates}[6]{%
	\setmydatenumber{datetoday}{#4}{#5}{#6}%
	\setmydatenumber{diffdays}{#1}{#2}{#3}%
	\addtocounter{diffdays}{-\thedatetoday}%
	\ifnum\value{diffdays}>0
		\def\diffbefore{in }%
		\def\diffafter{}%
	\else
		\def\diffbefore{}%
		\def\diffafter{}%
		\setcounter{diffdays}{-\value{diffdays}}%
	\fi
	\setcounter{diffyears}{\value{diffdays}/365}%
	\setcounter{diffdays}{\value{diffdays}-365*\value{diffyears}}%
	\setcounter{diffmonths}{\value{diffdays}/30}%
	\setcounter{diffdays}{\value{diffdays}-30*\value{diffmonths}}%
	%
	\diffbefore
	\ifnum\value{diffyears}=0
	\else
		\ifnum\value{diffyears}>1
			\thediffyears\space years\ignorespacesafterend
		\else
			\thediffyears\space year\ignorespacesafterend
		\fi
	\fi
	\ifnum\value{diffmonths}=0
	\else
		\ifnum\value{diffyears}>0
			,
		\fi
		\ifnum\value{diffmonths}>1
			\thediffmonths\space months\ignorespacesafterend
		\else
			\thediffmonths\space month\ignorespacesafterend
		\fi
	\fi
	\diffafter
}