Date Calculator is an easy-to-use tool which will quickly tell you the elapsed time between any two specified dates.
Launch the program and by default it'll set the first date to today, the second to December 25th, and so immediately you'll see the time to Christmas specified as days, weeks and months.
You can then specify other dates just by selecting them on the program's calendars, and the calculation will update right away. If there's a date you want to use regularly - a birthday, say - then this can be added to the "Jump to" list, so you can select it in a couple of clicks. And there's even an offset feature, so you can figure out, say, the number of days until three weeks after your wedding anniversary.
Please note, despite claiming to be a shareware package during installation, Date Calculator is actually a free tool: click the About button once installed for confirmation.