DEV Community

Blackmare01wolf
Blackmare01wolf

Posted on

Tkinter project: Simple Interest calculator

#python #tkinter #showdev

Introduction

This project is a Simple Interest Calculator built using Python’s Tkinter library, which provides a graphical user interface (GUI) for users to input values and calculate simple interest. It's designed to help students and beginners understand basic GUI development and financial calculations in Python.

Explanation

Tools Used:

  • Python — Programming language
  • Tkinter — GUI toolkit included in Python's standard library

Code Breakdown:

1. Importing & Creating the Window 

from tkinter import * b = Tk() b.minsize(800, 600) b.maxsize(800, 600)
Enter fullscreen mode Exit fullscreen mode
  • Tk() initializes the main window.
  • minsize and maxsize fix the window size to 600x600 pixels.

2. Interest Function 

def Interest(): try: P = int(e1.get()) # Principal  R = int(e2.get()) # Rate  T = int(e3.get()) # Time  I = (P * R * T) / 100 e4.delete(0, END) e4.insert(0, str(I)) except ValueError: e4.delete(0, END) e4.insert(0, "Invalid Input")
Enter fullscreen mode Exit fullscreen mode
  • Gets user input for Principal (P), Rate (R), and Time (T).
  • Calculates Simple Interest using: [ \text{SI} = \frac{P \times R \times T}{100} ]
  • Displays the result.
  • Handles errors if input is not a number.

3. Labels and Input Fields 

l1 = Label(b, text="Principal($):", font=("arial",15)) l2 = Label(b, text="Rate(%):", font=("arial",15)) l3 = Label(b, text="Time(year):", font=("arial",15)) l4 = Label(b, text="Simple Interest", font=("arial",15)) e1 = Entry(b, font=("arial",15)) e2 = Entry(b, font=("arial",15)) e3 = Entry(b, font=("arial",15)) e4 = Entry(b, font=("arial",15))
Enter fullscreen mode Exit fullscreen mode
  • Labels explain each input.
  • Entry boxes allow user input.

4. Button 

b1 = Button(b, text="Check Simple Interest", font=("arial", 15), command=Interest)
Enter fullscreen mode Exit fullscreen mode
  • When clicked, the button calls the Interest() function.

5. Placing the Widgets 

l1.grid(row=1, column=1) l2.grid(row=2, column=1) l3.grid(row=3, column=1) l4.grid(row=5, column=1) e1.grid(row=1, column=2) e2.grid(row=2, column=2) e3.grid(row=3, column=2) e4.grid(row=5, column=2) b1.grid(row=4, column=1)
Enter fullscreen mode Exit fullscreen mode
  • Positions all widgets using grid layout.

6. Mainloop 

b.mainloop()
Enter fullscreen mode Exit fullscreen mode
  • Starts the GUI application loop so the window stays open.

Full code 

from tkinter import * b = Tk() b.minsize(800, 600) b.maxsize(800, 600) def Interest(): try: P = int(e1.get()) R = int(e2.get()) T = int(e3.get()) I = (P * R * T)/100 e4.delete(0, END) e4.insert(0, str(I)) except ValueError: e4.delete(0, END) e4.insert(0, "Invalid Input") l1 = Label(b, text="Principal($):", font=("arial",15)) l1.grid(row=1, column=1) l2 = Label(b, text="Rate(%):", font=("arial",15)) l2.grid(row=2, column=1) l3 = Label(b, text="Time(year):", font=("arial",15)) l3.grid(row=3, column=1) l4 = Label(b, text="Simple Interest", font=("arial",15)) l4.grid(row=5, column=1) e1 = Entry(b, font=("arial",15)) e1.grid(row=1, column=2) e2 = Entry(b, font=("arial",15)) e2.grid(row=2, column=2) e3 = Entry(b, font=("arial",15)) e3.grid(row=3, column=2) e4 = Entry(b, font=("arial",15)) e4.grid(row=5, column=2) b1 = Button(b, text="Check Simple Interest", font=("arial", 15),command=Interest) b1.grid(row=4, column=1) b.mainloop()
Enter fullscreen mode Exit fullscreen mode

Result

Conclusion

This Simple Interest Calculator demonstrates how Python's Tkinter can be used to create interactive desktop apps. It's perfect for beginner coders, especially students, to understand:

  • How functions and GUIs work together
  • How to collect and validate user input
  • How to perform basic mathematical operations in Python

You can expand this project by adding:

  • Compound Interest calculations
  • Input validation for negative numbers
  • A clear/reset button for fields

Top comments (0)