Crunching the numbers: Should we be overpaying our mortgages or investing instead?

An interesting topic that is hotly debated in the personal finance circle. With interest rates at their lowest point for decades, this often turns into a duel between emotions and maths.

Let battle commence!

First up, US advice isn’t going to fly here.

Mortgages are yet another area that the US does differently to the UK. If you’re coming here with US centric advice burning your ears, you’re probably going to end up confusing yourself. Let’s clear up the differences.

  1. US mortgages are typically fixed for a lot longer than UK mortgages. Fixed term and variable mortgages exist in both ecosystems, but a fix for the life of the loan is not uncommon in the US. In the UK the longest fix traditionally on offer is about 10 years long (and you’ll usually pay heavily for this). This makes a big difference to the numbers.
  2. The terminology is a tad different. In the UK we call finding a new interest rate, provider or borrowing more “remortgaging”. In the US a “remortgage” doesn’t really exist, they refer to this as “refinancing”.
  3. Because US mortgages tend to have such longer fixed terms, they typically have to pay a lot more to swap products or lenders – often referred to as “closing costs”. In the UK we are free to swap about without fees once our fixes expire (unless you choose a product that has a fee of course!).
  4. LTV (loan to value) matters for both countries, but matters more for us in the UK because, you guessed it, we remortgage a lot more. Calculating your LTV bracket and planning around this can play heavily into your numbers.
  5. PMI (private mortgage insurance) does not exist in the UK but is compulsory for US mortgages that have an LTV above 80%. Yep you heard that right, in the US you need to pay for a special form of insurance if you have anything less than a 20% deposit. Once again, this will impact the numbers.

With that out of the way and hopefully cleared up, we can move onto examining the question at hand:

When does it make sense to overpay a mortgage?

To best address this we need to understand what actually happens if you overpay a mortgage. For those of you that are lucky enough to be home owners, you may notice that the terms of your mortgage allow you to “overpay”. This is usually capped to a certain % of the balance for fixes and unlimited for tracker products. For almost every mortgage taken out in recent memory, an overpayment does one of three things:

  1. It immediately reduces the outstanding principal on your mortgage, thus reducing the interest accrued on the life of the loan, regardless of your mortgage type.
  2. It will then either:
    1. Reduce your monthly payments by a set amount based on your overpayment.
    2. Reduce your mortgage term (the amount of time left until the mortgage is paid off).
    3. Some combination of the two above, usually defaulting to option 1 then option 2 when the fix ends.

From this information we can conclude that overpaying your mortgage earns you a total return exactly equivalent to your mortgage interest rate. This means that if you overpay your mortgage and your mortgage interest rate is 2.5%, this has exactly the same yield, in terms of return, as saving cash into a 2.5% interest rate account.

Simple? Sort of.

What return do I get by overpaying my mortgage?

Think of it this way:

Suppose you have a £150,000 mortgage, on a 25 year term, currently fixed for 5 years at a 2.5%. You’re contractually obligated to pay £673 every month for the first 5 years. If you’ve got a spare £200 each month you could pump this directly into your mortgage, effectively choosing to pay £873 a month. Where would this get you after 5 years?

Without the overpayment your 5 year fix would end with a balance owing of: £126,993

With the overpayment your 5 year fix would end with a balance owing of: £114,225

Looks good right? To be mortgage free all the sooner! But look a little closer under the hood. The difference between the two values (£12,768) shows you just how hard your money worked for you in this 5 year period. You put in £200 a month of your own cash for 5 years or £12,000. That means, in this scenario, your contributions returned you £768 which is exactly the same as letting your money grow at 2.5% interest in a savings account. Try it out on a compound interest calculator if you don’t believe me. The numbers will be very close.

As of writing this article no savings accounts offer 2.5%, so in that regard overpaying your mortgage mathematically offers a better return than cash in the bank.

But there are significant drawbacks to consider.

Mortgages are very, very illiquid. Your home is not a savings account.

Overpaying into modern mortgages is a little different than it used to be. Certain lenders such as Nationwide used to set up an “overpayment reserve” that meant if you overpaid previously, you could use this to fund future mortgage payments if times were tough. This is no longer the case as lenders have become a lot more strict. This means that overpaying a mortgage is highly illiquid. The only way to “get money back out of” a house (or an overpaid mortgage) is to either sell the property or remortgage and request a bigger loan. Which comes with a new interest rate and potentially a new fee. Getting, say, £300 back out of your previous mortgage overpayments is borderline impossible.

The question remains, can we make our money work harder for us?

Broadly, yes.

Enter the alternative, investing into stocks, shares, bonds, cash or ideally a mixture of all of these. By selecting products that will return a greater rate than the mortgage rate, you’ll be quids in! But of course it is never quite so simple.

A mortgage is a guaranteed rate of return. This means it is a risk free way of getting your money working for you. Insured cash deposits (e.g. current and savings accounts) are also guaranteed. As it stands, no savings accounts consistently beat mortgage rates, so this idea is out for now.

A diversified portfolio of bonds and stocks has a variable rate of return. Now we can see the risk factor come into play. By investing into the markets we will likely beat lower mortgage rates over the long term but we may lose out against them in the short term.

How much more could I earn by investing instead of overpaying?

The long returning average for a balanced portfolio of global bonds and equities is in the region of 6-9%. This is significantly greater than the return on the mortgage example above. If the individual above instead invested the monthly £200 for 5 years and achieved a return of 6% they would expect to have a final investment balance in the region of £14,023. This is a return of £2,023 – remember the mortgage? That returned only £768 in comparison. In this scenario, by choosing to invest, this individual would have earned an additional £1,255 for doing absolutely nothing. Seems like a no brainer, right?

Investing also has a significant liquidity advantage.

Remember how hard it was to get £300 out of your mortgage overpayment pot mentioned earlier? If you’d have invested into a stocks and shares ISA, this is as easy as selling £300 worth of your investments and waiting for the deal to complete. Within 3-5 days the money is in your bank account and can be used for anything from home improvements or holidays to paying the bills in times of job loss.

So the winner is clearly investing, right?

Yes. No. Maybe. Emotions are a big factor in this. People like to be debt free and have the security behind them of finally paying off a mortgage. But in terms of compounding you’re forcing yourself to have to save harder later in life.

  • Overpaying your mortgage is very safe but returns little.
  • Investing your money is very risky but will likely return a lot more.

Before we get swept away with this, we must remember that the markets are volatile and anything but a smooth ride. In such a short time frame (5 years) there is a 33% chance that we would actually be facing up to a net loss. We may have seen returns of anything between -50% and +150%. Nobody knows. This is where personal risk tolerance and a little bit of logical thought comes into play.

What does Mr Fox think?

This is purely my own opinion, so feel free to disagree. With that said, I believe that in the current environment it makes little sense to commit heavily to mortgage overpayments but some overpayments will always make sense to lock in that guaranteed return we mentioned.

My current mortgage rate is 2.64%. I firmly believe that the markets will return at least 4% over the next decade. 4 is greater than 2.64, so investing more is the logical play for me. I love the fact that I will be able to access the funds if I need to but I acknowledge that overpaying is a wise habit. This means I personally split my savings 90% to stocks and shares and 10% to overpaying the mortgage.

If my mortgage rate rises above my expected market return, I’ll rethink and commit more (perhaps everything!) to overpaying. But in our current environment of rock bottom rates, I won’t be doing that any time soon.

15 thoughts on “Crunching the numbers: Should we be overpaying our mortgages or investing instead?

    1. I thought that too (as they are my mortgage provider) but in closer inspection it seems that is only part and parcel of the older mortgages they issued… I could be wrong though! – Mr Fox


      1. My mortgage is 18 months old and has a reserve (which is where our next house savings is parked). Perhaps you had a very long fix or something?


  1. Why stop at investing rather than overpaying the mortgage, the same logic suggests we should borrow as much as we can to invest , let’s see if we can increase our mortgage, if we haven’t got a mortgage let’s get one….

    Borrowing to invest is a legitimate strategy but not for everyone…

    A guaranteed, low risk, tax free rate of return at your marginal rate is probably a sensible course of action for most people.

    Given we have had a 10 year bull market… let’s have a 50% market decline and then perhaps investing the excess cash would be a good potential investment but not many have the stomach for it in those circumstances….

    Personally I have it done twice with no decisive difference between the two approaches but given one of those periods covered 2000-2002 and 2007-2009 it required significant nerve to carry on.

    Leverage always appears more attractive when markets are going well…..

    Liked by 1 person

  2. My current plan is to not overpay but mentally allocate a portion of monthly investments to mortgage overpayments. I would only pay this off the mortgage after a long time when the accrued pot was enough to pay off the mortgage – when I’m in my early 50s hopefully. That way the risk of short term adverse market movement is reduced.

    I liked your comparison to the US particularly – very helpful for those of us who listen to certain US podcasts! I think another variable is that mortgage interest is still tax deductible there in certain circumstances?

    Liked by 1 person

    1. Yes you’re right about the interest being tax deductible in most circumstances. I have definitely heard that being pushed before but I didn’t know quite enough about it to include it – Mr Fox


      1. Yes, offset mortgages are brilliant & if more people fully understood them they would, I believe, be the most popular mortgage in the market.

        I’ve had them for close to 2 decades now: the mortgage is now fully offset so we actually pay £0 in interest each month & have the cash reserve there as our emergency fund.

        60% of this offset is our tax accrual for paying self assessment, so money comes in & out of the offset over the course of the year. Our mortgage tracks BOE base rate plus 1.09% for the life of the mortgage. Admittedly you won’t find a deal that good anymore: I remortgaged in late 2007 before the 2008 crash.

        Seems to me in an ideal world everyone’s mortgage would offset against at least their current accounts, which for nearly everyone in the UK achieve as near to zero % interest as the banks can get away with. But if all these (relatively) little amounts were offset against people’s mortgages they would still save thousands of the full term of a mortgage.

        Liked by 1 person

  3. A couple of points to finesse the article:

    1) Taxes need to be taken into account: if you can save using ISAs or are within the (UK) Interest allowance then the above holds true. If the income is taxable then you will need to add this in to your thinking.

    2) Mortgages in the UK are sensitive to LTV bands. If you are thinking ahead to your next rate in 2, 3, or 5 years time then it can make sense to overpay the mortgage to qualify for lower rates. Passing the 75% and 60% LTV thresholds in particular can mean your next rate will be much lower (of course you can pay savings against mortgage balance at the time it comes to switch).

    3) There are some fees in the UK for a remortgage (to a different lender) – Solicitors costs ~£500-750, and any fees on top (Brokers, product fees). Remaining with the same lender avoids Solicitors costs.

    Personally once I have got to the 60% LTV threshold and fixed my rate for 5 years then I will be switching more to Investing vs. overpaying.

    Liked by 1 person

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s