Several months ago we did an episode on Mac Power Users about managing subscriptions. During the show I explained that I have an Apple Numbers spreadsheet where I keep track of all of that information. I've finally gotten around to posting it. Below is a screenshot and at the bottom of this post is a download link.
The spreadsheet allows you to enter the name of the service and then whatever fee you’re paying. When you click the checkbox as to whether or not it's an annual subscription, the spreadsheet does some conditional computations to figure out the monthly cost and annual cost in the following two columns. Those are the key locations that you're going to be getting information about how much you’re spending. At the bottom of those columns you'll see how much you're spending per month and per year.
After that it’s just further information concerning the specific service like website, account number, contact information, and email. The point is you want to keep whatever you need in this database so you can cancel a subscription whenever you feel like it. The one thing I don't keep in this database is passwords. For that I go to 1Password.
Feel free to download, use, and modify. Let me know how it works for you.