How to Build a Simple Progress Bar in Tkinter

MatthewApr 7, 2025

Step 1: Set Up Your App Window

First, import the libraries and set up your main window:

import tkinter as tk
from tkinter import ttk
import time
import threading

root = tk.Tk()
root.title("File Downloader")
root.geometry("300x150")

Step 2: Add the Progress Bar

Let’s add a horizontal progress bar with a label to show percentage:

progress = ttk.Progressbar(root, orient="horizontal", length=250, mode="determinate")
progress.pack(pady=20)

progress_label = tk.Label(root, text="Waiting to start...")
progress_label.pack()

Step 3: Simulate a Download

We simulate the progress using a loop that updates the bar and label:

def download_simulation():
    for i in range(101):
        progress['value'] = i
        progress_label.config(text=f"Downloading... {i}%")
        time.sleep(0.05)
    progress_label.config(text="Download complete!")

Step 4: Use Threads to Keep the UI Responsive

Running the loop directly would freeze the UI. So, we run it in a thread:

def start_download():
    threading.Thread(target=download_simulation).start()

Step 5: Add a Button to Start the Download

Hook everything up with a button:

download_button = tk.Button(root, text="Start Download", command=start_download)
download_button.pack(pady=10)

Step 6: Start the App Loop

root.mainloop()

Step 7: Complete Code

import tkinter as tk
from tkinter import ttk
import time
import threading

def start_download():
    # Run the download simulation in a separate thread so the UI stays responsive
    threading.Thread(target=download_simulation).start()

def download_simulation():
    for i in range(101):
        progress['value'] = i
        progress_label.config(text=f"Downloading... {i}%")
        time.sleep(0.05)  # Simulate download time
    progress_label.config(text="Download complete!")

# Create the main window
root = tk.Tk()
root.title("File Downloader")
root.geometry("300x150")

# Create progress bar
progress = ttk.Progressbar(root, orient="horizontal", length=250, mode="determinate")
progress.pack(pady=20)

# Label to show progress percentage
progress_label = tk.Label(root, text="Waiting to start...")
progress_label.pack()

# Download button
download_button = tk.Button(root, text="Start Download", command=start_download)
download_button.pack(pady=10)

# Run the app
root.mainloop()

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