Welcome folks today in this blog post we will be building a loan calculator gui app inside pyqt5 in python. All the full source code of the application is shown below.

Get Started

In order to get started you need to install the following library using the pip command as shown below

pip install pyqt5

After installing this library make an app.py file and copy paste the following code

app.py

# importing required libraries 
from PyQt5.QtWidgets import *
from PyQt5 import QtCore, QtGui 
from PyQt5.QtGui import *
from PyQt5.QtCore import *
  
import sys 
  
  
class Window(QMainWindow): 
    
    # constructor 
    def __init__(self): 
        super().__init__() 
  
        # setting title 
        self.setWindowTitle("Python ") 
  
        # width of window 
        self.w_width = 400
  
        # height of window 
        self.w_height = 500
  
        # setting geometry 
        self.setGeometry(100, 100, self.w_width, self.w_height) 
  
        # calling method 
        self.UiComponents() 
  
        # showing all the widgets 
        self.show() 
  
    # method for adding components 
    def UiComponents(self): 
        # creating head label 
        head = QLabel("Loan Calculator", self) 
  
        # setting geometry to the head 
        head.setGeometry(0, 10, 400, 60) 
  
        # font 
        font = QFont('Times', 15) 
        font.setBold(True) 
        font.setItalic(True) 
        font.setUnderline(True) 
  
        # setting font to the head 
        head.setFont(font) 
  
        # setting alignment of the head 
        head.setAlignment(Qt.AlignCenter) 
  
        # setting color effect to the head 
        color = QGraphicsColorizeEffect(self) 
        color.setColor(Qt.darkCyan) 
        head.setGraphicsEffect(color) 
  
        # creating a interest label 
        i_label = QLabel("Annual Interest", self) 
  
        # setting properties to the interest label 
        i_label.setAlignment(Qt.AlignCenter) 
        i_label.setGeometry(20, 100, 170, 40) 
        i_label.setStyleSheet("QLabel"
                              "{"
                              "border : 2px solid black;"
                              "background : rgba(70, 70, 70, 35);"
                              "}") 
        i_label.setFont(QFont('Times', 9)) 
  
        # creating a QLineEdit object to get the interest 
        self.rate = QLineEdit(self) 
  
        # accepting only number as input 
        onlyInt = QIntValidator() 
        self.rate.setValidator(onlyInt) 
  
        # setting properties to the rate line edit 
        self.rate.setGeometry(200, 100, 180, 40) 
        self.rate.setAlignment(Qt.AlignCenter) 
        self.rate.setFont(QFont('Times', 9)) 
  
  
        # creating a number of years label 
        n_label = QLabel("Years ", self) 
  
        # setting properties to the years label 
        n_label.setAlignment(Qt.AlignCenter) 
        n_label.setGeometry(20, 150, 170, 40) 
        n_label.setStyleSheet("QLabel"
                              "{"
                              "border : 2px solid black;"
                              "background : rgba(70, 70, 70, 35);"
                              "}") 
        n_label.setFont(QFont('Times', 9)) 
  
        # creating a QLineEdit object to get the years 
        self.years = QLineEdit(self) 
  
        # accepting only number as input 
        onlyInt = QIntValidator() 
        self.years.setValidator(onlyInt) 
  
        # setting properties to the rate line edit 
        self.years.setGeometry(200, 150, 180, 40) 
        self.years.setAlignment(Qt.AlignCenter) 
        self.years.setFont(QFont('Times', 9)) 
  
        # creating a loan amount label 
        a_label = QLabel("Amount", self) 
  
        # setting properties to the amount label 
        a_label.setAlignment(Qt.AlignCenter) 
        a_label.setGeometry(20, 200, 170, 40) 
        a_label.setStyleSheet("QLabel"
                              "{"
                              "border : 2px solid black;"
                              "background : rgba(70, 70, 70, 35);"
                              "}") 
        a_label.setFont(QFont('Times', 9)) 
  
        # creating a QLineEdit object to get the amount 
        self.amount = QLineEdit(self) 
  
        # accepting only number as input 
        onlyInt = QIntValidator() 
        self.amount.setValidator(onlyInt) 
  
        # setting properties to the rate line edit 
        self.amount.setGeometry(200, 200, 180, 40) 
        self.amount.setAlignment(Qt.AlignCenter) 
        self.amount.setFont(QFont('Times', 9)) 
  
  
        # creating a push button 
        calculate = QPushButton("Compute Payment", self) 
  
        # setting geometry to the push button 
        calculate.setGeometry(125, 270, 150, 40) 
  
        # adding action to the calculate button 
        calculate.clicked.connect(self.calculate_action) 
  
        # creating a label to show monthly payment 
        self.m_payment = QLabel(self) 
  
        # setting properties to m payment label 
        self.m_payment.setAlignment(Qt.AlignCenter) 
        self.m_payment.setGeometry(50, 340, 300, 60) 
        self.m_payment.setStyleSheet("QLabel"
                                     "{"
                                     "border : 3px solid black;"
                                     "background : white;"
                                     "}") 
        self.m_payment.setFont(QFont('Arial', 11)) 
  
        # creating a label to show monthly payment 
        self.y_payment = QLabel(self) 
  
        # setting properties to y payment label 
        self.y_payment.setAlignment(Qt.AlignCenter) 
        self.y_payment.setGeometry(50, 410, 300, 60) 
        self.y_payment.setStyleSheet("QLabel"
                                     "{"
                                     "border : 3px solid black;"
                                     "background : white;"
                                     "}") 
        self.y_payment.setFont(QFont('Arial', 11)) 
  
    # method for calculating monthly  
    # and annually payments 
    def calculate_action(self): 
  
        # getting annual interest rate 
        annualInterestRate = self.rate.text() 
  
        # if there is no number is entered 
        if len(annualInterestRate) == 0 or annualInterestRate == '0': 
            return
  
        # getting number of years 
        numberOfYears = self.years.text() 
  
        # if there is no number is entered 
        if len(numberOfYears) == 0 or numberOfYears == '0': 
            return
  
        # getting loan amount 
        loanAmount = self.amount.text() 
  
        # if there is no number is entered 
        if len(loanAmount) == 0 or loanAmount == '0': 
            return
  
        # converting text to int 
        annualInterestRate = int(annualInterestRate) 
        numberOfYears = int(numberOfYears) 
        loanAmount = int(loanAmount) 
  
        # getting monthly interest rate 
        monthlyInterestRate = annualInterestRate / 1200
  
        # calculating monthly payemnt 
        monthlyPayment = loanAmount * monthlyInterestRate / (1 - 1 / (1 + monthlyInterestRate) ** (numberOfYears * 12)) 
  
        # setting formatting 
        monthlyPayment = "{:.2f}".format(monthlyPayment) 
  
        # setting text to the label 
        self.m_payment.setText("Monthly Payment : " + str(monthlyPayment)) 
  
        # getting total payment 
        totalPayment = float(monthlyPayment) * 12 * numberOfYears 
        totalPayment = "{:.2f}".format(totalPayment) 
  
        # setting text to the label 
        self.y_payment.setText("Total Payment : " + str(totalPayment)) 
  
  
  
# create pyqt5 app 
App = QApplication(sys.argv) 
  
# create the instance of our Window 
window = Window() 
  
# start the app 
sys.exit(App.exec())

Now if you execute the above python script by typing the below command as shown below

python app.py