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Investment Magic: The Power of Compound Growth

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by Irish Life Financial Services

Written by Irish Life staff

Guides  •  26 March 2025  •  5 min read

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In this guide, you'll learn

• What compound growth is and why it’s so important.

• How frequency and rate impacts compound growth.

• How to make the most of compound growth in investing.

So what is compound growth and why does it matter?

Compound growth is one of the most powerful financial forces in the world, and it’s especially important when it comes to investing.

Essentially, compound growth means that you generate returns on both your original investment as well as on any previous returns. That second part is extremely important.

Imagine you have a choice between one of two gifts:

  • €1,000,000 deposited into your bank account today, with 5% boost applied daily for 30 days – that’s a €50,000 top-up every morning.
  • €0.01 deposited into your bank account today and then doubled every day for 30 days – so on day two you’d have €0.02, and then €0.04 the next day, and so on.

It’s tough to turn down a million Euros with €50,000 a day on top. At the end of the 30 days, choosing €1m will give you a grand total of €3,500,000 in the bank. Not bad.

But now consider the power of compound growth. 

Unlike simple interest (where you only earn interest on your original money, like in the first gift), compound interest lets you earn interest on your interest. 

This snowball effect can have stunning results. In fact, you're going to wish you had chosen the €0.01 bank balance.

Compound growth can lead to huge returns.

Had you chosen that doubling €0.01, you’d be looking at a final figure of €5,368,709.12 – nearly a full €2,000,000 more than the €1m and daily top-ups.

Compound growth is one of the most powerful financial forces in the world.

The Rule of 72 for compounding

There is a formula to calculate compound growth: P(1+r/n)^(nt) where P is the starting amount, r is annual growth rate, n is interest frequency, and t is the number of years the investment is held.

But that’s pretty convoluted and a bit too much like hard work, so let’s just work with the Rule of 72.

The Rule of 72 basically tells you roughly how long it would take to double your money. Take the number 72 and divide it by the estimated growth rate – that’s how long doubling your money takes.

So at 6% interest, your money will double in 12 years (72/6 = 12). Easy.

Of course, the nature of investments means that you can’t predict annual growth. Even if you do get a 6% average growth rate over 12 years, it’s not going to be smooth and linear; there could be some 20% years and some -15% years, all averaging out to 6% annually.

That’s why it’s so important to remember that investing is a long-term game of patience. It’s not a get-rich-quick scheme – when done properly and with a little luck, it’s a “get a little richer slowly scheme”.

With compound growth, your money can work for you.

The magic of time: why starting early pays off

Let’s compare two investors: Early Eddie and Late Larry. Both of them decide to invest €5,000 a year at 7% annual returns, and both of them want to withdraw their cash at age 65.

The difference? Eddie starts at 25 and invests for 10 years before leaving his cash to sit and grow. Larry starts at 35 but invests for 30 years.

Here’s how it works out:

Early Eddie put in €100,000 less but has wound up with over €50,000 more.

Compound growth: frequency matters

One consideration with compound growth is how often growth or interest is applied.

Is the return annual (once a year), monthly (12 times a year), or daily (365 times a year)? 

The more often interest is added, the faster money grows. Imagine you invest €10,000 at 5% return for 10 years. Here’s what you have in three different scenarios:

  • Compounded annually: €16,288
  • Compounded monthly: €16,470
  • Compounded daily: €16,532

It’s not a gigantic difference over 10 years, but over a longer investment daily compounding can result in thousands of Euro extra.

Time in the market beats timing the market every time.

In other words, rather than trying to predict spikes and invest at the right time, starting early is the best strategy.

Remember the €0.01 that doubled every day? If you find an investment strategy that results in 100% daily growth you probably don’t need this guide, but hopefully that exaggerated example shows you that small investments over a long time can be extremely beneficial.

Investing is a game of patience.

How dollar-cost averaging works

Dollar-cost averaging (or Euro-cost averaging on this side of the Atlantic) is a fancy-sounding term for a pretty straightforward investment strategy:

  • Invest a small amount of money at regular intervals: you can invest as little as €100 a month with Smart Invest.
  • Ignore the ups and downs of the market: don’t think about buying low and selling high.
  • Let compound interest do the heavy lifting for you: remember, given enough time it’s magic!

The benefits of dollar-cost averaging

No stress over markets: nobody can predict when the markets will rise or fall, and this way you don’t even have to worry about it. You just invest your €100 a month and get on with life.
It builds discipline: you’re not just investing when you have spare cash or just when you fancy it. It’s a regular part of your financial strategy.
It smooths risk: because you invest the same amount, you buy more when prices are low and less when prices are high.

Battling inflation: the enemy of savings

One of the key reasons that we should be investing in Ireland is to stop “saving ourselves poorer.”

Many people keep their extra money in the bank, credit union, or some other low-interest account that generates little to no return. 

The issue with this is that while the money may be safe from the risks of a falling investment market, it is not safe from inflation.

Inflation refers to the increase in costs of goods and services over time – the recent cost-of-living crisis has thrown this into focus for many people. But even a more “normal” rate of inflation will decrease the value of your savings by a couple of percent each year.

We’ve discussed how compound growth is an incredibly powerful tool for growing money – well, inflation is the polar opposite. It’s compound anti-growth, and it can really whittle away your cash. Investments can be used to battle or potentially even outpace inflation, reducing or even negating the impact of inflation on your money.

Inflation is the enemy of compound growth

Make the most of compound growth

We’ve established already that the biggest ally of compound growth is time. Consistent investments, patience, and knowing just how long the long-term is will be your biggest assets.

Now let’s explore a few more strategies:

  • Finding your best investment.
  • Mastering consistency.
  • Avoiding major mistakes.

Choose the best long-term investment for you

We have some other guides regarding choosing the best fund for you and finding your risk tolerance, but it’s worth considering how you might want to invest to maximise compound growth:

  • Investment funds: these are a good balance of potential long-term growth at relatively higher returns. You can choose the level of risk and reward with which you are comfortable and have your investment managed by experts.
  • Bonds: these are a lower-risk investment, especially when diversified (i.e. invested across different bonds and not having all your eggs in one basket). The downside is that the ceiling for potential returns can often by lower.
  • Pension: many people don’t think of a pension as being an investment, but that’s exactly what it is. With the income tax relief on offer to eligible workers in Ireland, this could be your most fiscally sound investment choice.

Consistency is king: creating investment habits

Aesop wasn’t managing a Multi-Asset Portfolio of investments, but when it comes to one aspect of investment strategy his tortoise and hare story was dead on: slow and steady wins the race.

You don’t need to have a huge amount of money to invest. Even €100 a month can build some substantial wealth if things go right and you’re happy to be consistent for decades.

Time really can equal money.

Tips for consistent investing

Err on the side of caution – a smaller amount you can invest each month is better than a larger amount you can only spare half the time.

Use a direct debit to make your investment payments on payday. That way, the money is invested without you even having to think about it.

Use round-up apps or similar tools to squirrel away extra cash each month to then invest. This is a great way to make setting money aside less effort.

One thing to note is that you should probably have your financial ducks in a row before you think about investing, especially if you want to invest more than the bare minimum. Make sure you’re free from high-interest debt and have an emergency fund built before you start your investment journey.

The biggest investment mistakes to avoid

Starting too late: there are very few investors who think “I wish I had waited longer to invest!” We’ve established how starting early with a small amount is significantly better than starting late with more.
Panic pausing: the nature of investments is that they can go down as well as up. But over time, sensibly invested money tends to generate returns over and above inflation. If you panic and sell at the first sign of trouble, compounding can’t work its magic. Trust the process.
Ignoring inflation: the lower-risk investments like bonds and higher-interest savings accounts can be tempting. After all, no one wants to lose their money in the markets. But beware – if these returns can’t beat inflation, losing money becomes inevitable. It’s key to balance your risk and reward.

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