import tkinter

tmr = 0

def count_up():
    global tmr
    tmr = tmr + 1
    label['text'] = tmr
    root.after(1000, count_up)

root = tkinter.Tk()
label = tkinter.Label(font = ('Times New Roman', 80))
label.pack()
root.after(1000, count_up)
root.mainloop()