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Interest rates: Why fixed is broken

A fixed rate means your monthly payment won’t change when the prime lending rate rises or falls. So what’s not to love? A lot, actually.

When signing up for a loan, you are usually quoted an interest rate relative to the prime rate. For example, you may be offered a rate of prime plus 0.5%. This is known as a variable rate – because the rate will vary according to the prime lending rate.

Sometimes you are also given the option of a fixed interest rate. With this option, the rate will not change, and is fixed for the duration of the loan (or, if the loan is longer than five years, then the fixed rate is usually fixed for a period of five years). With a fixed rate, even if the prime lending rate is increased or decreased, the repayment amount will remain unchanged.

So if you are presented with the option of a fixed rate or a variable rate, which one should you go for?

I am putting the answer right near the top of the article, so that if anyone is looking for the short version, here it is:

It is pretty much always better to choose a variable interest rate instead of a fixed interest rate.

The bottom line is this – at the beginning of a loan, only a small amount of the repayment value goes towards the principal debt. The rest of the payment goes towards interest. So it is in your interest (see what I did there?) to have a lower rate at the start of a loan rather than at the end of the loan.

And this is where the problem with a fixed interest rate comes in …

The fixed interest rate you will get is almost always going to be higher than the variable interest rate you would get. One of the big cheeses over at bond originator Ooba, Kay Geldenhuys, explains it thus: “Banks hedge their own risk of the interest rate going up by only allowing the consumer to fix their repayments at a rate higher than the one they were paying before.”

So a fixed rate means you will have a higher interest rate at the start of the loan – the part where it hurts the most!

Okay now I can hear you shouting the same reasoning the lenders use when presenting a fixed interest rate option: ‘The fixed rate makes you secure in the knowledge that your monthly payment will not change. Even if interest rates rise, your monthly repayment amount will be unaffected.’

And yes, this is true. But what they fail to tell you is that if the interest rate did rise, even aggressively, it will take a few years for the value of the variable rate to increase and overtake the value of the fixed rate. By the time that happens, the damage caused by the higher fixed interest rate at the start of the loan is only partly offset by the gains of the lower fixed interest rate at the end of the loan.

That may sound complicated, so I think it is time for some examples …

Fixing your interest rate in a rising interest rate environment 

Consider someone taking out a R100 000 loan over five years (60 months). They get two options – a variable rate of prime + 0.5% (currently equal to 10.75%) or a fixed rate of 12.75%.

Let’s start off by loading the dice heavily in favour of the fixed interest rate option. Let’s assume that the South African Reserve Bank jacks up the repo rate every six months by 0.5% for the duration of the loan. In other words, the variable rate will move from 10.75% at the start of the loan all the way up to 15.25% by the time the last payment is made (we are playing into the usual reason given for fixing your interest rate: that the interest rate can rise and you can end up on a higher interest rate.)

The result of this scenario is summarised below:

  Fixed interest (12.75%) Variable interest (starts at 10.5% and increases by 0.5% every six months until 15.25%)
Total repaid R135 751.80 R134 184.67
Total interest R35 751.80 R34 184.67

You can see that even with the extremely aggressive increases in the prime lending rate – resulting in the variable interest rate ending up a full 2.5% higher than the fixed rate – the variable interest rate option still ends up costing around R1 500 less!

Now let’s look at the monthly instalments for each scenario. 

Source: Author

You will notice that, in the beginning, the instalments for the variable option are much lower than the fixed option (R2 137 versus R2 237). The variable interest rate instalments then get bumped up with each interest rate hike, until it overtakes the fixed interest rate repayments.

But visually, you can see how the big savings in instalments at the start of the loan are only partially offset by the additional costs at the end. 

Source: Author

Or to put it another way, the next chart shows the interest paid per month for the variable and fixed interest rate loans. 

Source: Author

Again, you can see the damage done by the higher fixed interest rate at the start of the loan. The lower interest paid at the end of the loan is not enough to catch up!

So, even in a bit of a worst-case scenario, the variable interest rate option comes out tops.

I want to address one last counter-argument in this scenario – the repayment amount at the end of the loan is higher for the variable interest rate option (R2 281.86) than for the fixed interest rate option (R2 262.53). This can cause someone to overspend on their budget, right?

Okay, let me quickly smash this one out of the park:

  1. If an extra R20 (or even R200 for that matter) a month on debt repayments is going to sink your budget, you are over-extended and should not be taking the loan in the first place!
  2. By the time the variable interest instalment overtakes the fixed interest instalment, three years would have passed. In that time you should have received a few inflation-related salary increases (heck, if you were smart enough to choose the variable interest option, I would say you would have even got a promotion by then). 

Okay, I think that’s enough about the rising interest rate scenario. But because I don’t think it’s fair to only check the worst-case scenario, let’s see what happens if interest rates just plod along sideways, or better still, go in your favour?

Fixing your interest rate in a flat interest rate environment

Using the same parameters as the first example (a loan of R100 000 over 60 months with a fixed rate of 12.75% or a variable rate of prime +0.5 (so 10.75%) let’s see what happens if the prime rate remains unchanged. I think the result is obvious (a loan at 12.75% is going to be way more nasty than a loan at 10.75%), but here are the actual numbers:

  Fixed interest (12.75%) Variable interest (starts at 10.75% and remains at 10.75%)
Total repaid R135 751.80 R129 707.72
Total interest R35 751.80 R29 707.72

In a scenario where rates remain unchanged, you would have been R6 000 better off by going with a variable rate.

Fixing your interest rate in a falling interest rate environment 

Finally, let’s see what happens for that same loan if the prime interest rate decreased. Let’s say the variable interest rate starts at 10.75% and then the prime rate is decreased by 0.5% every year.

  Fixed interest (12.75%) Variable interest (starts at 10.75% and decreases every year by 0.5%, until 8.75%)
Total repaid R135 751.80 R126 381.83
Total interest R34 225.92 R26 381.83

You would have been over R7 900 better off by going with the variable rate! Win!

Time to hit the turbo 

Here is something else to consider about the whole fixed-versus-variable decision.

If we consider our loan example, the two options were:

Fixed at 12.75% – starting instalment R2 237

Variable at prime + 0.5% – starting instalment R2 137

The fact that you even considered the fixed option, means that you could afford an instalment of R2,237. Yes? 

But since you know that the variable interest rate is the way to go, your instalment is now only R2 137.

Time to hit the turbo button on that loan – take the extra R100-or-so saving (you could afford the higher instalment remember?) and pump it back into the loan. This will save you even more interest and reduce the loan term by a few months.

Score again on the variable interest side!

So when should you fix your rate? 

In the above examples, it was clear that going with the variable interest rate was the better option in a rising, flat and falling interest rate environment. So is there ever a time to fix your interest rate?

I suppose a case could be made if the fixed rate was only slightly above or even below the variable rate quoted (I don’t think this has ever happened). But even then, I would be very hesitant.

Always remember, lenders are not in the business of messing themselves over. If they are offering a fixed rate, you can be damn sure that the odds are weighted in their favour (and not yours). The bank is taking on some risk by fixing your rate, and you can be sure that they expect to be rewarded for sticking their neck out. Your fixed rate will always reflect this extra reward they expect.

Finally, one last quote to put the final nail in the fixed-interest-rate coffin (found in this article on

“It is important to note that studies have found that over time, the borrower is likely to pay less interest overall with a variable rate loan versus a fixed rate loan.”

Just go with the variable rate!

This article was republished with permission from Stealthy Wealth. The original can be found here.

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Excellent article. Well laid out. A must read for everybody.

His website and archive of articles is a must-read for the man in the street wanting to get his personal finances in order.

A very well articulated piece. I’ve never been a fan of fixed.

Lending to others looks for me a better life happy situation as asking for a loan. The latter assume this happening by retirement age. If not, who cares.

Another thing to remember;
As you rightly pointed out, most fixed loan terms are 5 or so years. So even in a rapid rising interest rate environment, just as you start to really enjoy the benefits of fixing the rate, the terms are up for renegotiation. The bank will then have the privelege to set a new fix rate, again higher than the prevailing prime rate, as was the case 5 years ago, and you start behind again.

You never truely get the benefit of a long period where the prime rate is higher than the fixed rate.

Sounds just like the Discovery Above Threshold Benefit. The threshold is multiplied by the number of members and you will never get to the point where it pays anything. The principle is to sell a nice concept that has actually almost no value.

Many people do reach the ATB. For those who don’t, pick an option which doesn’t have it. Simple!

@Wendy, I did after my company allowed flexibility in how medical aid contributions are paid. Typical scenario family of 3 with one person having heavy expenses. ATB will be reached in December. Great idea for single persons who have a medical history. Not useful for families who are mostly healthy.

Very well written article. Just one mistake in the headings of the first table – 10.5% instead of 10.75%. Compound interest on a loan is never your friend, no matter how smartly the bank package it. So, the sooner you can eat away at the capital of the debt, the better. Even make higher payments than required if you can. As Einstein said: Compound interest is the eighth wonder of the world – those who understand it, earn it, and those who don’t, pay it.

Perhaps a different take: if one wants to reduce your (20yr) bond interest, how about re-negotiating with the bank to have the bond re-structured over 15 yrs (i.e. bringing it down from 20 yrs).

One will pay more per month (which assumed is the intention to pay more than the basic bond), but my argument is, IF there is a potential interest-rate shock hitting SA (like Moody’s downgrade, or SA default on Eskom debt, etc) then increased interest rate will be re-calculated by the bank on a shorter 15 yr bond…so the “interest-component leverage” will be less. The worst is people that have 30 yr bonds…yes, you pay less in instalment, but any future rate increase will be even more sensitive on the homeloan cost.

Comments from anybody within the banking sector perhaps? (One downside could be new bond-registration fees(?) when a bond term is restructured? Not sure.)

One can reduce the period of payment by increasing your bond payments. I paid off my bond in seven years. Maintained a low balance to allow me to access the bond when in trouble (access bond). I worked for 3 years at a night club as a cashier and used the earned money to reduce my bond. I also put in my bond at least 30% of my yearly bonus. After paying off the bond I use half the bond amount and saved the other half. Today I am 68 and am reaping the benefit of the savings and living in a paid up house.

Article lacks historical perspective.

SA interest rates are now at historical lows since we joined the FIAT world in the 1970’s.

If we experience 1980’s or 1990’s style rise to 20+% interest rates, you’d be dreaming you went fixed. Almost every global recession has seen interest rate spikes in SA.

If you betting on low interest rates to stay for another 30 years, then you are automatically assuming a rosy global economy and no emerging market shocks. Wishful thinking in my opinion.

I agree that this article lacks the breadth of historical and geographical perspective. Fixed rates have their place, particularly in a benign interest rate environment where the risk of inflation and rampant rate rises offsets the potential benefit of rate cuts. One trades the potential benefit of future rate reductions for the certainty of protection from any increases – this certainty is worth something for many borrowers, particularly those starting out on a mortgage, where they may well have maxed out their affordability at the beginning and therefore cannot sustain the shock of an interest rate increase. It’s obvious that one pays a premium over the floating rate to fix the rate – that’s the price of the certainty. The longer you fix for, the higher the premium. It’s daft to dismiss a whole suite of interest rate products because they don’t suit the current circumstances in South Africa. A lot of financial journalists and commentators haven’t observed full economic cycles – the last decade has been anything but a guide to the future.

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