• Skip to main content
  • Skip to footer
MENUMENU
  • Home
  • About Us
    • Our Philosophy
    • Choosing a Financial Planner
    • Legal and Regulatory
    • Team
    • Careers
    • Contact Us
  • Our Services
    • Financial Planning
    • Ongoing Financial Guidance
    • Portfolio Management
  • Financial Planning Basics
    • Continuing Care Retirement Communities (CCRCs)
    • Retirement Planning and Cash Flow
    • Social Security
    • Taxes
    • Insurance & Risk Management
    • Investments
    • 401(k)
    • Real Estate
    • College
    • Liquidity
    • Divorce
    • Estate Planning
    • Sensible Updates
  • Resources
    • The Types of People We Help
    • Webinars
    • Blog
    • Videos
    • Financial Planning Guidebook
    • Continuing Care Retirement Communities Guidebook
    • Primers
    • Financial Planning Links
    • Client Links
    • Financial Planning for Older Adults
  • Contact Us
Sensible Financial Planning

Sensible Financial Planning

Follow Us

  • Facebook
  • LinkedIn
  • Twitter
  • YouTube
Client Links

Call Us Today
781-642-0890

Debunking Investing Rules of Thumb, Part 2 

by
Gyb Spilsbury
CFP® - Financial Advisor

August 27, 2025

The picture shows two one-way signs to symbolize the fact that there are different ways to look at investing.

As I said in my previous article, we at Sensible Financial are not big fans of financial rules of thumb. Every situation is different and demands careful analysis and critical thinking. One-size-fits-all rules of thumb may be helpful to some, but they can be poor advice for many others.  

My first Rules of Thumb article focused on saving and accumulation. This is part 2, geared more toward retirement and withdrawals. 

“Let’s assume that people live in retirement on 80% of what they are used to.” 

This took hold several decades ago as a rough estimate, and we find it to be too rough. It tries to capture the notion that retirees do not have mortgage or retirement savings “costs” like they did when earning. Therefore, they can live on less than they used to. 

This rule of thumb might only work for people whose retirement coincides with paying off their mortgage. For those who paid it off years ahead of retirement, or who carry one into retirement, this assumption does not match their actual cash flow. The rule of thumb would indicate that they reduce their lifestyle, which is a bold assumption. Although spending composition may change over time, not many people are keen to reduce their lifestyle in retirement, and in fact, many wish to spend more in the early years of retirement on things like travel. 

Permanent life insurance as a good way to build wealth 

Too many people have been sold various forms of permanent life insurance that are not suitable. Salesmen often say something like “this policy will build cash value that will provide a fantastic nest egg for retirement.” Unfortunately, it is an incredibly expensive and inefficient way to invest and build wealth.  

With these policies, some premium dollars go toward building the cash value. In other words, each premium payment partially pays for life insurance and is partially for investment, with the insurance company doing the investing for you. Those insurance expenses eat into the investment returns, often resulting in slow growth. In addition, the cost to invest—either by way of fund or insurance company fees—can range from 1-2%. Far greater than a simple index fund that charges 0.08%, for example.  

We suggest not combining your investment and insurance needs; it’s better to tackle separately. It is often best to buy term life insurance to protect loved ones, and it is less expensive to invest without the “help” of an insurance company. 

The 4% safe withdrawal rule 

In the 1990s, advisor William Bengen came up with this guideline: that one can draw 4% in year one of retirement (then increase with inflation as time goes on). Although there is some truth to this, it should only be used as an initial guideline. It is by no means right for everyone, and more specific analysis and planning is required.  

First, some people can spend more than this but restrain themselves. Some may do so specifically to support the next generation (or a family member in need), while others simply may not be spending as much as they could and might wish to.  

Second, this rule does not fully take into account that drawing from your portfolio as a newly retired 65-year-old is much different than drawing as a 90-year-old. Adverse effects, like high inflation and/or poor market returns, can be especially devastating for those in early retirement. In addition, the degree to which these things damage the portfolio depends on how the portfolio was constructed. For example, a portfolio with inflation-protected bonds would support one’s retirement much more robustly through high inflation years than a portfolio with nominal bonds. 

These are three rules of thumb often heard. They can serve as a starting point, but should be taken with a grain of salt. Your situation demands deeper thought and analysis, as everyone’s situation is different. If you have questions, please feel free to contact your advisor.  

Photo by Brendan Church on Unsplash

More articles by Gyb Spilsbury Filed Under: Investments Tagged With: financial planning, invest, investing

Footer

Services

  • Financial Planning
  • Financial Guidance
  • Portfolio Management

About Us

  • Our Philosophy
  • Team

Resources

  • Blog
    • The Types of People We Help
  • Financial Planning Guidebook
Sign up for our Newsletter

Follow Us

  • Facebook
  • LinkedIn
  • Twitter
  • YouTube

Locations

Massachusetts

203 Crescent Street, Suite 404

Waltham, MA 02453

Phone: (781) 642-0890
Fax: (781) 810-4830

 

California

600 B Street, Suite 300

San Diego, CA 92101

Phone: (619) 573-4131​

Sensible Financial Planning has been acquired by Beacon Pointe Advisors as of October 1, 2025. To access services, resources, or support, please visit https://beaconpointe.com/financial-advisors/ma/waltham/wama/. Important disclosures for clients can be found by visiting https://beaconpointe.com/disclosures/. Advisory services offered through Beacon Pointe Advisors, LLC, a registered investment advisor.

Disclaimer

This content reflects the opinions of Sensible Financial®. We may change it at any time without notice. We provide this content for informational purposes only. Although we endeavor to keep the information up-to-date and correct, we make no representations or warranties of any kind, express or implied, about the completeness, accuracy, reliability, suitability for a particular purpose or availability with respect to the website or the information, products, services, or related graphics contained on the website for any purpose. We do not intend the information contained in this website as investment advice and we do not recommend that you buy or sell any security. We do not guarantee that our statements, opinions or forecasts will prove to be correct. Past performance does not guarantee future results. You cannot invest directly in any index. If you attempt to mimic the performance of an index, you will incur fees and expenses which will reduce returns. All investing involves risk. You can lose any money you invest. There is no guarantee that any investment plan or strategy will succeed.

More important additional information and full disclaimer.

Copyright © 2026 Sensible Financial · All Rights Are Reserved
Legal Disclosure