As long as you have an awl or even a large nail in your home, you can easily add an extra hole to your belt. If you want to make sure it blends in with the others, create a template with some painter's tape.
As how-to site ManMade DIY demonstrates, to create a hole template for your belt, place a piece of painter's tape along the belt over the hole. Use a nail or even a pen to poke through the tape where the holes in the belt are. Once you've done this for all the holes, peel the tape off and shift it down the belt by one hole. The last hole in the tape should perfectly line up with where your new hole should be.
Once you have your template in place, you can use a leather hole punch, an electric drill or even an awl or nail and a mallet to punch the new hole. It's a relatively easy leather modification that lets you keep your favourite belt, even if starts to get too loose. Check out the post below for the full instructions on how to add another hole to your belt.
How to: 3 Ways to Punch a Hole in a Leather Belt [ManMade DIY]