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:
[related: PMT formula syntax and examples]
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)
|Add a Scroll-bar Control|
|Excel 2003||Excel 2007|
Once selected, just add the control to spreadsheet by clicking anywhere.
Step 2: Set Properties for this Scroll-bar
To set the properties for the scrollbar control, right click on it and go to “format control” option. Now go to “Control” tab.
Here set minimum and maximum values for the scroll bar. To keep our model simple, just set minimum as 35 and maximum has 500.
Also, select a cell to link the scrollbar. When you do this, excel links the scroll bar to the selected cell. So whenever scroll bar is updated the cell gets updated too (and vice-a-versa). See this illustration:
Step 3: Add Remaining Scroll bars
Repeat the same steps for 2 other scroll bars. One for interest rate and one for loan tenure.
Make sure you set the minimum and maximum values in a reasonable range.
Step 4: Plug the values in to PMT formula
Now that the scroll bars are ready, just write the PMT formula. Assuming you have linked scroll bars like this:
- Loan amount in cell A1
- Interest rate in cell A2
- Loan tenure (years) in cell A3
The formula will be,
Remember, PMT returns value in negative numbers (as it is the amount we need to pay, not get). But you can make it positive (for display purposes) by multiplying it with -1 like this
Step 5: Play with your Model
Now your mortgage payment calculator is ready. You can play with it by testing various combinations and finding monthly payments. You can easily see what happens when you increase loan tenure or decrease interest rate.
Download Excel Mortgage Payment Calculator
Here is the excel mortgage payment calculator file. Download and play with it.
Bonus – Making an Amortization Schedule
You can easily extend this model to add an amortization schedule to see how much of each monthly payment is towards principal and how much is for interest.
- You can calculate principal portion for any month using PPMT formula like this
=PPMT(R/12,M,N*12,P). Here “M” is the month for which you want principal amount.
- You can calculate interest portion for any month using IPMT formula like this
Do you love form controls?
Do you use form controls in your spreadsheets? I find them pretty intuitive and use them wherever I can. I have made many complex spreadsheet models easy to understand and work with by just adding form controls. The beauty is that, they require no programming or anything. You just add them and link them to a cell.
What about you? Do you love form controls? Where do you use them most?
Learn More about Excel Form Controls:
- Make a comparison chart using scroll bars
- Create a check box in excel
- Make a donut bar chart using form controls
- More form control examples
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