Enjoy 20% off all plans by following us on social media. Check out other promotions!

Mortgage Calculator

Ex-Meta Staff Engineer

Build a simple mortgage calculator widget that takes in a loan amount, interest rate, loan term, and calculates the monthly mortgage payment, total payment amount, and total interest paid.


  • The user should be able to enter:
    • Loan amount ($)
    • Annual interest rate (%). This is also known as the annual percentage rate (APR)
    • Loan term (in years)
  • Using the inputs, the calculator should compute the following and display the results to the user:
    • Monthly mortgage payment
    • Total payment amount
    • Total interest paid
  • If a non-numerical string is entered into any input field, the calculator should display an error message. Additionally, the calculator should handle any other invalid inputs that may arise.
  • Round the result amounts to 2 decimal places.

The last two requirements might not be given to you during interviews, you're expected to clarify.

The formula for calculating the monthly payment is:

M = P(i(1+i)n)/((1+i)n - 1)

  • M: Monthly mortgage payment
  • P: Loan amount
  • i: Monthly interest rate (APR / 12)
  • n: Total number of payments (loan term in years x 12)

Here's an example of Google's mortgage calculator (you might need to be in the US for it to appear):

Google's mortgage calculator widget


This question is adapted from FrontendEval's Mortgage Calculator.

View solution