I spend less than 5% of my annual net pay on clothes. I am not into fashion, but I certainly don't dress like a bum. I bargain shop for clothes: Nordstrom Rack, Ross, sale sections at Gap and Banana Republic, etc. I never pay full price for any piece of clothing. For example, I recently purchased a brown suede jacket at Nordstrom Rack for $36. It was regularly priced at $128, then a markdown of 25%, and then a final mark down of something like 40%.
If you're not that excited about fashion like me, I would say anywhere from 5-10% of your annual income. If you like to wear nice clothes and that is important to you, spend more on clothes and cut back in a different area of your budget.
Enjoy your life in retirement: wear sweatpants all the time and be comfortable!!!