from tkinter import *
from tkinter import ttk

def progress(currentValue):
    progressbar["value"]=currentValue

def change_label(value):
    try:
        label.destroy()
    except:
        pass
    label = Label(root)
    label["text"] = str(value) + "%"
    label.place(relx = 0.5, rely = 0.3, anchor = "center")


root = Tk()
root.geometry("400x400")

progressbar = ttk.Progressbar(root, orient = HORIZONTAL , length = 200, mode = 'determinate')
progressbar.place(relx = 0.5, rely = 0.2, anchor = "center")

progressbar["value"] = 0
progressbar["maximum"] = 100

value = 0

while True:
    for i in range(100):
        value = value + 1
        progressbar.after(100, progress(value))
        progressbar.update()
        change_label(value)
    value = 0

root.mainloop()