In the legal world, we often have to calculate the number of days between two dates. In my practice, I run into this frequently in determining postjudgment interest and calculating real estate tax prorations.

I use a custom spreadsheet created by my mathematically inclined wife. TechnoEsq offers some other solutions. In his post, he talks about a WordPerfect macro that you can download. If you are not using WordPerfect, he also points you to TimeAndDate.com, which will perform these calculations for you as well. He also points out that if you are a Mac user running Leopard, you can create a widget out of the TimeAndDate webpage.

The point is that there are a variety of resources available. You should never be manually calculating these dates.