How to present a character counter for a byte restricted text input?

I have a text input which restricts input of characters when a certain byte limit has been met. I want to indicate this using a character counter which increases or fills up (in case of a progress bar or circle).

If the text input had a character based limit, this would have been straightforward. But a byte limit makes it tricky.

Should I assume a worst case scenario and set a max byte for each character (eg. 4 bytes) and then calculate the number of characters remaining? Or is there a better way to present this?