I have been wanting to post this for awhile, and I am finally getting around to fill everyone in on the details of how to look at some basics of mortgage financing, specifically the interest only loan compared to a normal fully amortizing loan.
Fully Amortizing Loan
So what is a fully amortizing loan? Well amortization on a loan is the amount of principal or loan repaid. So if you had a $100 loan with a monthly interest rate of 10% and you made a payment of $50 at the end of the month the interest paid would be $10 and amortization or principal of $40, so the next month you would have a loan of $60.
Obviously people are not buying homes for $100 but the above example was simple to explain amortization. So take that example and add fully amortizing and it means that a loan will be fully paid off at the end of the agreement. So if you have a 30-year fully amortizing loan it would mean that the amortization of principal amount paid down after 30 years would be equal to the original amount of the loan. This would mean that the loan is paid off and you would own your home fully.
This was traditionally how homes were bought, with 30-year fully amortizing home loans.
The transaction would occur as follows: A house would be bought for $625,000 with a mortgage for $500,000 and a down payment of 20% or $125,000. The monthly payment would be $2,998 (based on 6% interest and not including taxes or insurance). At the end of 30 years the home would have no loan against it and the monthly payments would be zero.
(Please note: the principal paid down is initially small as the interest portion of the payments accounts for approximately 90% of each monthly payment in the first 5-10 years).
Interest Only Loan
Interest only loans are not as straight forward as they sound. The initial prospect of an interest only loan is that a borrower would only pay interest. So with the same $500,000 loan at 6% the monthly payment would be $2,500 or $498 less per month than a fully amortizing loan. So of course that sounds great, in fact with an additional $500 you could put a lot of food on the table, pay for a car loan, etc.
The problem resides in the fact that these loans are not interest only forever. Eventually the bank will require some amortization or principal repayment so that the loan is repaid. A typical interest only loan is between 5-10 years of interest only with 20-25 years of amortization to finish off the loan.
So if you took out a 10-year interest only loan with a 20 year amortization on the back end the payments would be as follows. For the first ten years you would have a monthly payment of $2,500 and in year eleven the monthly payments would jump up to $3,582 or an increase of over $1,000 (or an increase of about $584 compared to the fully amortizing 30 year mortgage). This occurs because you are repaying the same $500,000 loan over 20 years instead of 30.
The other risk is what happens if after 7 years you want to sell the home and the value has declined by 25%. If this occurs the home would be worth $468,750 and the loan balance on the interest only would be $500,000 forcing the home seller to come up with $31,250 to repay the loan.
If the fully amortizing loan was used than after seven years the home value would be the same $468,750 but the loan to be repaid would be $446,680. So the home owner would receive $22,070 in cash after the sale of the home and repayment of the loan. So while the initial down payment amount of $125,000 would have declined substantially in either case the interest only loan would require additional money to repay the loan while the fully amortizing loan would allow some cash to be received in the sale of the house even with a substantial 25% decline in value.
The flip side of the above argument is that in the first three years the fully amortizing loan only pays down principal by just under $20,000 which is just under the $21,024 saved by lower payments with the interest only loan. So if a house did not decline in value and was sold than you could have used the additional savings with the lower monthly payments to make better investments.
Should You Consider an Interest Only Loan?
There are instances where it might make sense to take on an interest only loan.
1. You want to purchase a home and are confident your income will increase to meet the increase in payments when the interest only option decreases
2. You have a feasible alternative investment for the savings garnered by a lower monthly payment.
3. A large percentage of your pay is given in the form of annual or quarterly bonuses and want the flexibility of a interest only option where you can pay down principal with the large bonus payments and have lower required monthly payments.
4. Although dubious, if you are very confident that home prices will go up, it could make sense to have an interest only loan. (Please note that I would never advise this as a reason to take out an interest only loan as no one can tell the future for sure, especially in a 5-7 year time frame).
Conclusion
I hope that helps discuss how the interest only mortgage works compared to a fully amortizing (traditional mortgage). I have an excel worksheet that you can use to calculate loan payments (including insurance and tax) if you are interested. I can also answer questions about negative amortization loans, adjustable rate mortgages, etc if people are interested. Just leave me a comment and I will get back to you.
-Thor