The Rule of 72: A Simple Way to Understand How Your Money Could Grow
Understanding how investments may grow over time does not need to involve complicated formulas. One of the simplest tools investors can use is the Rule of 72.
The Rule of 72 is a quick calculation designed to estimate how long it could take for an investment to double in value, assuming a consistent annual rate of return. While it is only a rule of thumb and cannot predict actual investment performance, it can be a useful way of demonstrating the potential impact of long-term compounding.
For anyone building savings, investing for retirement or considering their wider financial plans, the Rule of 72 can help put investment returns into a more understandable context.
What is the Rule of 72?
The calculation is straightforward:
72 ÷ annual rate of return = approximate number of years for your money to double
For example, if an investment achieved an average return of 6% a year:
72 ÷ 6 = 12 years
On this basis, £50,000 invested today could theoretically grow to around £100,000 after approximately 12 years, assuming a consistent 6% annual return and no withdrawals.
If the same investment achieved 8% a year:
72 ÷ 8 = 9 years
The money could therefore theoretically double in around nine years.
Of course, investment returns are rarely consistent from one year to the next. The value of investments can rise and fall, and you may get back less than you invest. Nevertheless, the Rule of 72 provides a useful illustration of why time and compounding can be so important.
A financial adviser can also help you understand how investment fees and charges affect the return you actually receive, rather than focusing solely on headline investment performance.
Book a meeting with an adviser to discuss how long-term investment growth could fit into your wider financial plan.
Why compounding matters
The real lesson behind the Rule of 72 is not necessarily the calculation itself. It is the power of compounding.
Compounding occurs when investment growth generates further growth. Instead of earning a return only on the money originally invested, you potentially earn returns on previous investment gains as well.
Consider £100,000 growing at an average of 6% a year. Using the Rule of 72, it could theoretically double approximately every 12 years.
That means it could broadly become:
-£200,000 after 12 years
-£400,000 after 24 years
-£800,000 after 36 years
These figures are purely illustrative and assume a consistent return with no withdrawals, charges or tax. Real-world investment performance will vary.
However, they demonstrate why starting earlier can have such a significant impact on long-term financial outcomes.
When looking for the best approach to investing, a financial advisor should consider your objectives, timescale, capacity for loss and attitude towards investment risk rather than simply selecting investments based on the highest historical returns.
The Rule of 72 and your pension
The Rule of 72 can be particularly useful when thinking about retirement planning.
If you are decades away from retirement, there may potentially be several periods during which your investments could double. This helps demonstrate why relatively small differences in long-term returns can eventually translate into substantial differences in the value of a pension.
For example, someone aged 30 investing for retirement at age 66 has a 36-year investment horizon. At an illustrative 6% return, the Rule of 72 suggests their money could theoretically double approximately three times during that period.
This is also why unnecessarily delaying pension contributions can be costly. Contributions made earlier potentially have more time to benefit from compounding.
An independent adviser can help assess your pension alongside your other assets and determine whether your existing investment strategy remains appropriate for your objectives.
Investment returns are only part of the picture
It can be tempting to assume that achieving a higher investment return is always preferable. In practice, investment decisions involve balancing potential returns against risk.
An investment expected to deliver 10% a year would theoretically double much more quickly than one returning 5%. However, achieving higher potential returns normally involves accepting greater investment risk and potentially larger falls in value.
The appropriate investment strategy therefore depends on factors including:
-how long you expect to remain invested
-how much investment risk you are comfortable taking
-how much loss you could financially withstand
-whether you are likely to need access to your money
-your tax position
-your wider assets and liabilities
-your retirement and estate planning objectives
A financial adviser offering a comprehensive service should consider these factors together rather than viewing investment performance in isolation.
Book a meeting with an adviser if you would like to review whether your current investments remain suitable for your long-term objectives.
How inflation changes the calculation
The Rule of 72 can also be used to demonstrate the effect of inflation.
Instead of calculating how quickly an investment might double, you can use the same principle to estimate how long it could take for prices to double.
If inflation averaged 3%:
72 ÷ 3 = 24 years
In very simple terms, something costing £50,000 today could therefore cost approximately £100,000 in 24 years if prices increased consistently at 3% each year.
This highlights one of the risks of holding too much long-term wealth in cash. While cash can be valuable for emergency reserves and short-term spending requirements, its purchasing power may gradually fall if interest rates do not keep pace with inflation.
A certified adviser or appropriately qualified financial advisor can help explain how inflation affects longer-term objectives, including retirement income and the amount of protection you may need to maintain your family’s financial security.
The impact of charges
The Rule of 72 can also highlight why investment charges matter.
Suppose an investment portfolio produces a gross return of 7%, but the total effect of product, platform and investment costs reduces the return received by the investor to 6%.
Using the Rule of 72:
72 ÷ 7 = approximately 10.3 years
Compared with:
72 ÷ 6 = 12 years
A difference that initially appears relatively small can become increasingly important when compounded over several decades.
That does not mean the cheapest investment solution is automatically the right one. Cost should be considered alongside diversification, investment management, tax efficiency, risk and the overall financial planning proposition.
Anyone searching online for a top financial adviser or trying to find financial adviser support should therefore look beyond investment performance alone and understand both the costs being paid and the value of the advice being received.
Where the Rule of 72 falls short
The Rule of 72 is useful because it is simple, but that simplicity also creates limitations.
Investment markets do not produce identical returns every year. There will inevitably be periods when investments fall as well as rise, and the sequence in which those returns occur can be particularly important for someone withdrawing money during retirement.
The calculation also does not automatically account for taxation, investment charges, withdrawals or additional contributions.
For more detailed financial planning, cashflow modelling can provide a much richer picture by allowing different assumptions around inflation, investment performance, retirement income and future expenditure to be considered together.
A useful starting point, not a financial plan
The Rule of 72 is ultimately a useful educational tool rather than an investment strategy.
Its greatest value is demonstrating just how powerful long-term compounding can potentially be. It also reinforces an important principle of financial planning: time can be just as important as the amount invested or the return achieved.
For investors with long-term objectives, staying invested through different market conditions and maintaining an appropriate diversified portfolio can often be more important than continually attempting to identify the next highest-performing investment.
As a UK independent financial advisory firm, we believe investment decisions should sit within a broader financial plan that considers your goals, tax position, pensions, income requirements and attitude towards risk.
Book a meeting with an adviser to explore how your investments could contribute towards your longer-term financial objectives.
The value of investments can fall as well as rise, and you may get back less than you invest. Past performance is not a reliable indicator of future performance. The figures used in this article are illustrative only and do not represent guaranteed investment returns. Tax treatment depends on individual circumstances and may change in the future.
