Excel Tip: Calculating Interest

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Microsoft Excel is an ideal tool for calculating the cost of borrowing money, but are you doing so in the most efficient manner? In this article, I'll describe how you can use the CUMIPMT function to calculate interest expense for a loan, whether for a month, a year, or the length of the loan - all within a single worksheet cell. I'll also show you how to add an amortization schedule to any workbook with just a couple of mouse clicks.

Before I describe the CUMIPMT function, let's first take a look at the PMT function, which calculates the payment amount for a loan. PMT has 3 required and 2 optional arguments:

rate - The interest rate for the loan expressed as a monthly rate.

nper - The length of the loan in months.

pv - The amount being borrowed, also referred to as the present value.

fv - This optional argument allows you to specify a future value if a balloon amount is due at the end of the loan. Omitting this argument implicitly states that the loan is to be paid down to 0.

type - This optional argument allows you to specify if payments are made at the beginning of each period, or you can omit the argument to indicate that payments are made at the end of each period. You may also specify 0 in this position to explicitly indicate that payments are made at the end of each period.

Figure 1: The PMT function calculates the monthly payment for a loan.

As shown in Figure 1, a monthly payment of $586.04 for 36 months is required to pay back $20,000 at an interest rate of 3.5 percent. The PMT function always returns a negative amount because Excel sees the payment as an outflow. I omitted the 2 optional arguments, so in this case, the PMT function assumes the loan is paid to 0 and payments are made at the end of each period.

You construct formulas using CUMIPMT in a similar fashion to PMT, but in this case, all 6 arguments are required:

rate - The interest rate for the loan expressed as a monthly rate.

nper - The length of the loan in months.

pv - The amount being borrowed, also referred to as the present value.

start_period - The starting month from which to calculate interest on the loan. Use 1 to calculate interest from the start of the loan, or 13 to calculate interest for just the second year of the loan.

end_period - The ending month through which to calculate interest on the loan. Use the same value as the nper argument to calculate interest for the life of the loan, or 24 to calculate interest for just the second year of the loan.

type - Specify 0 to indicate that payments are made at the end of the period, or 1 for payments made at the start of the period.

Figure 2: The CUMIPMT function computes total interest for all or part of a loan.

As shown in Figure 2, the CUMIPMT function shows that borrowing $20,000 at 3.5 percent for 36 months will cost $1,097.50. Although not shown, the cost for the second year of the loan is $368.55. To calculate the principal paid back for a given portion of the loan, use CUMPRINC, which utilizes the same sequence of arguments as CUMIPMT.

As you can see, it's possible to use worksheet functions to calculate interest and principal for all or part of a loan without building out a full-scale amortization schedule. However, when one is needed, right-click on any worksheet tab and then choose Insert, as shown in Figure 3. Click on the Spreadsheet Solutions tab, and then double-click on Amortization Schedule. 

Figure 3: Add an amortization table to any workbook with just four clicks. 

About David Ringstrom, CPA

David Ringstrom

David H. Ringstrom, CPA, is an author and nationally recognized instructor who teaches scores of webinars each year. His Excel courses are based on over 25 years of consulting and teaching experience. His mantra is “Either you work Excel, or it works you.” David offers spreadsheet and database consulting services nationwide.

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By rajesh
Jun 26th 2015 01:11

thanks for this advice ...now no more salute to any banker......

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By Al
Jun 26th 2015 01:11

Thank you! Very helpful.

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By MIlan
Jun 26th 2015 01:11

thanks :)

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By Abhi
Jun 26th 2015 01:11

Very clear. Thanks a lot. I am able to create my own sheet now

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By Jason
Jun 26th 2015 01:11

Is the result the present value of the interest cost over the life of the loan? Or is it the future value (at the end of the loan) of all of the interest accumulated over the life of the loan? Do I need to do an additional adjustment find the present value? Thanks for this explanation.

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By David Ringstrom
to johnoneil
Jun 26th 2015 01:11

Jason,

Great question! Yes, CUMIPMT does return the present value of the interest earned over the life of the loan. To prove it out, right-click on any worksheet in Excel, choose Insert, and then double-click on Loan Amortization in the Spreadsheet Solutions tab. This will add an amortization table to your workbook, and you can run the same numbers as you used with CUMIPMT to see that the results are the same.

David

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By chad
to lobrien
Jun 26th 2015 01:11

What about if the loan with the interest will be due on the date given and the borrower does not paid for the remaining amount on that date, what would be the formula to get the penalty for the existing days/month?

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By Sunil Fulara
Jun 26th 2015 01:11

I WANT THE SAME FOR CALCULATION HOW TO CALCULATE

Details
of Projected Interest Expense

Actual
Projected

Month
Week 1
Week 2
Week 3
Week 4
Week 1
Week 2
Week 3
Week 4

Particulars
Oct-14
Nov-14
Nov-14
Nov-14
Nov-14
Dec-14
Dec-14
Dec-14
Dec-14

Interest expense(Gross)

Other borrowing costs

Total
-
-
-
-
-
-
-
-
-

Less: Interest capitalised

Interest Expense(Net)
-
-
-
-
-
-
-
-
-

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By john
Jun 26th 2015 01:11

if I know the cost(3,915) and the principal (19,800) what is the actual interest for 2.5 years?

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By Chad
Jun 26th 2015 01:11

What about if the loan with the interest will be due on date given and the borrower does not paid for the remaining amount on that date, what would be the formula to get the penalty for the existing days/month?

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By David Ringstrom
to dspinks41
Jun 26th 2015 01:11

In that case the borrower isn't paying down principal any more, they're simply accruing interest on the unpaid balance. One approach would be to take the interest rate and divide it by 365. Multiply that figure by the unpaid balance times the number of days that the loan is past due. So on an unpaid balance of $10,000 at 4.5% interest of $55.48 would be due when the balance is 45 days old. There are lots of different ways to write a loan contract, so make sure you review the promissory note to determine treatment of missed payments or balloon balances.

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By Lori
Jun 26th 2015 01:12

How can a balloon payment be included in CUMIPMT calculation? I am looking for the total interest amount for loan with regular monthly payments and balloon at the end. Thanks so much for any advice.

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May 5th 2016 19:32

Good Afternoon,
Is it possible to show how this can be done using rule 78 to calculate the inst amount?

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