The Rule of 375

Amyr Rocha Lima

6 min read

Retirement planning is a topic that often leaves many feeling overwhelmed and uncertain about the future.

However, there are some simple heuristics, or rules of thumb, that can help you begin to navigate the complexities of financial planning for retirement. One such rule is the 'Rule of 375'.

In this blog, we'll simplify the intricacies of the 'Rule of 375', its mathematical roots in the renowned '4% Rule', and why it might just be an invaluable tool in your retirement planning toolkit.

Understanding The Rule of 375

The 'Rule of 375' is a clever adaptation of the well-known financial planning guideline called the '4% Rule'. To truly grasp its significance, let's explore how it transforms one rule into another.

In 1994, Bill Bengen, an American financial planner, embarked on a data-driven journey. He examined decades of stock market and bond return statistics and emerged with a revelation: retirees could safely commence their retirement by withdrawing 4% of their nest egg in the first year of retirement, adjusting this withdrawal annually to account for inflation.

According to Bengen's findings, this strategy would be reasonably sustainable for 30 years, which, incidentally, somewhat matches the average life expectancy for couples retiring in their 60s.

Here's the essence of the '4% Rule':

Suppose you have £1,000,000 tucked away for retirement. According to the '4% Rule', you can withdraw 4% of that in the first year, which amounts to £40,000. Each subsequent year, you adjust this withdrawal to keep pace with inflation, preserving the purchasing power of your withdrawals.

In essence, the '4% Rule' helps you determine a sustainable annual withdrawal that your retirement nest egg can support over 30 years.

Now, picture this scenario: Say, instead, you want to withdraw £50,000 annually from your retirement savings, and you want this withdrawal to be 4% of your total wealth. To achieve this calculation as a multiplier (instead of division), consider the reciprocal of the 4% withdrawal rate, which is 1 / 0.04 = 25.

Hence, when you multiply £50,000 by 25, you get £1,250,000.

The 'Rule of 375' takes this concept and adapts it to a monthly perspective, making it more relatable, as most of us think of our expenses as a monthly figure. Additionally, it also makes a rough allowance for 20% tax, as most of us think of our expenditure net of taxes.

Let's go through the math.

Starting with the 25 multiplier from above, to transition the '4% Rule' from annual to monthly, we multiply 25 by 12 months in a year: 25 * 12 = 300.

To account for taxes at a nominal rate of 20%, we divide this by 0.8 - i.e.: 300 / 0.8 = 375.

And voilà, the 'Rule of 375' is born!

This rule of thumb provides a practical estimate of the retirement nest egg required today to maintain your desired monthly spending throughout a 30-year retirement.


Imagine Sarah, a retiree with dreams of travelling the world and enjoying her retirement to the fullest.

After working through her vision of her ideal retirement, Sarah calculates that she needs £3,500 per month to cover all her expenses and live comfortably.

To gauge the investment pot required to sustain this level of spending, Sarah can simply multiply this monthly spending requirement by 375.

£3,500 * 375 = £1,312,500

So, using the 'Rule of 375', if Sarah were retiring today and aiming to spend £3,500 per month for the next 30 years, she’d need to have a retirement nest egg of just over £1,300,000.

By following this guideline, Sarah can start to make informed decisions about her savings and investment strategy to reach her retirement goals.

Benefits of The Rule of 375

Understanding the 'Rule of 375' is important because it allows you to start translating your retirement goals into practical financial terms.

This rule of thumb takes into account the fact that most people think of their expenses on a monthly basis, and incorporates a rough allowance for tax at 20%, as most of us think of our expenditure net of taxes.

By using this rule of thumb, you can start gauging what you'll need to do to better plan for your retirement and ensure that you have the financial security you need to enjoy some of your most cherished life goals.

Common Mistakes to Avoid

While the 'Rule of 375' provides a useful estimate, it's essential to recognise its limitations.

One common mistake is relying solely on this (or any other) rule of thumb without considering other factors that can impact your retirement plan, such as financial market fluctuations, additional income sources one might be entitled to in retirement (such as the State pension), and the ever-changing nature of one's own retirement.

To avoid this mistake, it's advisable to work with a Certified Financial Planner®. This certification is the only globally recognised mark of excellence in financial planning and is a degree level qualification.

Working with a CFP® professional can provide you with more in-depth analysis, helping you tailor your retirement plan to your specific circumstances, ensuring a more accurate and reliable financial strategy for your retirement.

But use this heuristic and take a moment to evaluate your current financial status.

How much have you stowed away for your retirement, and at what rate are you adding to it? Does your current financial trajectory align with your vision for retirement? If not, knowing the gap is the first step in bridging it.

Frequently Asked Questions (FAQ)

Q: Can I rely solely on the 'Rule of 375' for my retirement planning?

A: While the 'Rule of 375 provides a rough estimate of the size of the nest egg you need today to maintain your desired monthly spending throughout a 30-year retirement. It's advisable to also consider other factors and work with a Certified Financial Planner® to build a more comprehensive retirement plan.

Q: Is the 'Rule of 375' suitable for everyone's retirement planning?

A: The 'Rule of 375' is a simplified guideline. Individual circumstances vary, so it's essential to customise your retirement plan based on your unique financial situation and goals.

Q: How often should I revisit my retirement plan using the 'Rule of 375'?

A: It's a good practice to review your retirement plan at least annually, and when significant life changes occur, to ensure it remains aligned with your goals.

Final Thoughts

In conclusion, the 'Rule of 375' can be a valuable tool that gets you thinking about retirement planning by estimating the nest egg needed to maintain your desired monthly spending throughout a 30-year retirement.

While it offers a helpful starting point, it's important to recognise its limitations and seek professional guidance to create a more comprehensive retirement strategy.

By using this rule of thumb, you can take the first steps towards achieving financial security during your retirement years.

If you're ready to take control of your retirement planning and want a more detailed and personalised strategy, consider contacting our team of Certified Financial Planner® professionals. We can provide expert guidance tailored to your specific financial goals and help you navigate the complexities of retirement planning with confidence.

Your future self will thank you for it!

For a more detailed discussion on this topic, please feel free to contact us. Our team are always available to answer your questions and to help you with any of your financial planning needs. Here’s what we offer: A cup of coffee… and a second opinion.

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