Like many things a kilt with or without a belt it is a matter of choice. If you look at some of the older pictures the kilt is worn up just under the rib cage. In this case a belt is not possible. The more recent practice (20 years) a belt is common, especially a Clan belt for formal wear.

In "So You're Going To Wear The Kilt" (3rd revised edition) page 71, "Belts are now being worn any time one chooses."

I perfer a belt but this is personal...so if the belt fits wear it...if you want.

Richard-