Dr. Scroll-bar Mortgage Calculator or: Why you should not be borning and use form controls
Today we will build a mortgage payment calculator using excel. But we will not build a boring excel sheet, we will build a mortgage calculator that is easy to play with.
A mortgage payment is a monthly installment that you pay towards a loan. Any mortgage loan will typically have,
- loan amount
- duration of the loan (also called as tenure of mortgage) in years
- interest rate (APR) per year
Given these 3 parameters, we can easily determine the monthly installment amount (this will be the same amount for all months during loan tenure)
We are going to use Excel’s form controls (more on this below) to build a mortgage payment calculator like this:
Why you should not be boring and use the form controls
A form control is a button or check box or scrollbar or some other click-able thing you see in Windows. Do you know that you can add the very same controls to Excel spreadsheet to make the it interactive?
- instead of asking a user to enter “yes” or “no” in a cell, you can ask them to click a check box.
- instead of taking “age” in a cell, you can use a scroll bar and set the values from 0 to 100.
This way of
gathering inputs is more fun, engaging and interactive.
Now that you find form controls hot and attractive, lets proceed and make a house loan payment calculator.
How is mortgage payment calculated?
As I said above, any mortgage (or housing loan) will have 3 parts – loan amount (p), loan tenure (n) and annual interest rate (r).
Given the values of P, N and R, we can find the monthly payments using Excel’s PMT formula like this:
We are dividing interest rate (R) by 12 since R is annual interest rate and we make monthly payments.
We are multiplying loan duration (N) with 12 since we are going to make monthly payments.
Making the mortgage calculator in Excel
We will use scroll-bar controls to take numeric inputs required (P,N and R) for the payment calculation. And we feed these values to PMT formula to find the monthly installment amount.
Step 1: Add a Scroll-bar Control
We will use this scroll bar to take “loan amount” input. To keep it simple, we will ask users to enter input in ‘000s. So, if the loan is $120,000, the input should be 120.
First add a scroll-bar form control to your excel sheet. To do this go to Developer Ribbon > Insert > Scroll-bar Form Control in Excel 2007. In Excel 2003 use View > Toolbars > Forms and select Scroll-bar control. (related: enable developer toolbar in excel 2007 )