Too Much of a Good Thing?: Mortgage Prepayments

This is a guest post from Gary Foreman. Gary is the editor of The Dollar and various e-newsletters including Financial Independence. Financial Independence is designed to walk step-by-step with you as you take control of your finances and achieve financial freedom! For more on mortgage prepayments read How Mortgage Prepayments Work.

I am trying to find the best way to really take advantage in reducing our mortgage to save on interest paid. We are in our home for 5 years with a 30 yr fixed @ 6.1% rate. Payment is $1500 mo. We are now sending in our regular payment weekly by dividing 1500 by 4. On top of that we are sending in $400 to $500 weekly to add to principal. We did not know if dividing the original payment by 4 if it would make a big difference since it is getting there early in weekly amounts. We would sure appreciate advice and help. – TR

Wow! TR is to be congratulated on her dedication to paying off the mortgage quickly. But, let’s see if all those extra payments are reducing the length of her mortgage.

Hopefully, TR has already taken the first step. That’s to make sure that her mortgage allows for prepayments without penalty. Most mortgages do allow it, but it’s good to be certain. If not, they’ll take all her payments and just apply them to the next regular due date. Effectively making all her early payments an interest free loan to her mortgage company!

Let’s talk about what TR is trying to do. By sending one quarter of her monthly payment in each week she could be reducing the amount of interest owed and that would mean that more of her payment goes to reducing principal.

Basically it’s a math problem. We’ll break it down into easy to understand pieces. Beginning with the interest rate.

Typically we talk about interest rates on an annual basis. In this case 6.1% per year. But in reality it’s a daily rate. In this case 6.1% divided by 365 days or 0.0167% or 0.000167 per day.

So the mortgage company multiplies the principal (i.e. the amount that TR still owes on the mortgage) by 0.000167 each day. That amount is added to the amount owed.

Suppose that TR’s mortgage is $100,000 (probably not a realistic number, but a nice round one to work with). For each day TR will owe an additional $16.71 in interest. So for a 30 day month she’d owe $501.37 in interest on the $100,000 mortgage amount.

If her payment were $1500 roughly one third would go to paying the interest owed ($501.37) and two thirds ($1500 – $501.37 = $998.63) would go to reducing the principal.

What happens when TR sends in one quarter of her payment 3 weeks early? The amount she’s sending in is $375 ($1500 / 4 = $375). The amount of interest to borrow $375 for 21 days is $1.32 ($375 * .000167 * 21 days = $1.32). That’s true no matter how big or small the mortgage principal is.

The second weekly payment would save $0.88 ($375 * .000167 * 14 days = $0.88). The third weekly payment would save $0.44 ($375 * .000167 * 7 days = $0.44).

What about the extra principal that TR is sending in weekly? Let’s say that she sends in $500 per week. That $500 is worth $0.58 per week.

So sending in all those weekly payments really isn’t saving TR much money. In fact, if she’s mailing them the cost of the envelope and postage is consuming much of the savings. That, and her time has some value, too.

Now some of you will have noticed that by paying weekly TR has added the equivalent of a full monthly payment each year. But she doesn’t need to make weekly payments to get that effect. All she has to do is to keep adding extra to each payment for principal reduction.

And, in that area TR does have the right idea. By adding $400 or $500 a week to reducing the principal, she’s making a major dent in the length of her mortgage.

Calculating the effects of additional principal prepayments is a little more difficult. The reason is that they reduce the amount of interest owed next month. So the amount of next month’s payment that goes to pay interest is reduced and the amount that goes to pay principal is increased. And, that effects the next month’s payment even more. And, that the month after, etc.

Suppose that TR combines her extra principal into one $2,000 payment per month. She’ll reduce the amount of interest owed by $10.16 ($2000 * .061 / 12 = $10.16). So her next monthly payment will in effect be prepaying an additional $10.16 of principal. And, that will make the payment after that even more effective. Just that one $2,000 prepayment would shorten the life of the mortgage by one and a half years.

Unless you’re a math fiend, it’s easier to use a prepayment calculator you find on the net. One that I like is found here.

So what should TR do? Probably skip the weekly payments. They’re having a very minimal effect and increase the chances for a clerical foul-up at the mortgage company. But, TR should continue to make monthly principal prepayments. They’ll make a major difference in the length of her mortgage.

Keep on Stretchin’ those Dollars!

Photo by pnwra

13 thoughts on “Too Much of a Good Thing?: Mortgage Prepayments

  1. Great advice and very well explained. I had once thought that paying weekly would save a boatload of money, but when I ran the numbers it didn’t really do anything. Plus, you make a great point about possible clerical errors possibly causing issues that just aspect don’t make this worth it. But definitely adding extra to the princinpal is the right way to go!
    .-= Money Beagle´s last post: The Most Important Shopping Tip To Remember =-.

    1. Mortgage/loan companies have definitely gotten better at recognizing that many people want to pre-pay, but my experience is also that it can be a hassle to make the extra payments apply correctly. Like you, I would stick with once monthly.

    1. I’m curious to see the other side of the coin too–keeping money out of the house as the best approach (and not only for the “traditional” reason of investing the difference). Maybe I’ll tackle this in a few weeks.

  2. I believe paying extra principal can be a smart thing to do but there are a few questions I would ask myself first:

    1. How much do I have in my contingency fund? Do I have enough to cover my expenses for 3 months? 6 months? 12 months? Money tied up in your home is not liquid. I blogged about this awhile back (

    2. Am I taking full advantage of my pre-tax investment vehicles (401K for example). Remember that the extra principle you are paying is with after-tax dollars.

    What is the opportunity cost? For example, sometimes saving money to pay cash for a reliable used car is a better use of the ‘extra’ principal payment. YMMV.

    Another question to ask. Am I paying PMI (Private Mortgage Insurance)? What is my threshold to get out of it?
    In most cases, once you pay your loan down to 78% of the original principal balance, you can get your lender on the horn and get rid of PMI.

    Once you pass these thresholds (especially a well funded contingency fund) your extra principal payments will make even more sense, save you interest and shorten your mortgage term.

    Best of luck you you!

    .-= WR´s last post: Book Review: The Elements of Investing by Burton Malkiel and Charles D. Ellis =-.

    1. 2 great points, WR. I did not consider the after-tax nature of extra payments. 🙂

    1. On the other hand, I wonder if that $0.58 really does make a difference compounded over 30 years… 😉

  3. Great explanation of the “benefits” of making weekly payments. I think WR makes some good points about when it might not be advantageous to pay extra on the principle, but this post simply makes the point that the best way to pay off a mortgage is to pay extra on the principle and not make several payments each month.

    Making those weekly payments is something that I assumed wasn’t all that beneficial, but you have explained why. Thanks!
    .-= Joe Plemon´s last post: Airstream Saga Continues: Jan and I Second Guess Our Decision =-.

  4. I have been paying extra on my mortgage for 14 years. I chose the method of just paying extra each month. This is easy to do and it allows for a lot of flexibility.

    Mathmatically, it may seem like there are better places to put money, instead of trying to save 5% interest on a mortgage. But, over the course of 30 years of compounding, it is a lot of money I will have saved.

    More important, is that I’m only six years away from paying it off and I will have cut 10 years off the loan. My ultimate goal is financial freedom and eliminating the mortgage is a huge first step.

  5. I’m starting to think that I am confused. I used to be in mortgage servicing, but I was in the foreclosure department. I wasn’t directly involved in applying payments but I did spend a lot of time helping explain things to our customers. Our loans did not contain a pre-payment penalty. If we received a payment that was less than the payment due, it was put in “suspense,” basically put aside until the rest of the payment arrived. We were not able to make any principal payments for a month until the regular payment had been made.

    In your example, the first three payments of each month wouldn’t be of any value as they would sit in suspense until the fourth payment arrived, thus making up a whole payment that could be applied to the account. Only in months in which five payments arrived would there be any principal payment. Depending on how you are submitting the payments, and how you are giving directions to the processing staff, that might end up in suspense or might be applied to principal. In our smallish office, we would call the customer and ask what they intended if it was not clear. In a big servicing center, you are much less likely to get that service.

    I’m not saying that our small bank did things the same way that all mortgage servicers do, but that is my experience. I would love to hear more about other people’s experience.

    Thanks for the post – very good.

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