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Supercharging the ‘4% rule’ to ensure a richer retirement

Despite being a giant in retirement planning, Bill Bengen is a humble chap.

He was a financial advisor in the US in the early 1990s trying to figure out how his clients, mostly Baby Boomers like him, needed to save for retirement to ensure they wouldn’t run out of money.

It was becoming a pressing question at that time because his generation was the first to have a long life expectancy in retirement.

Bengen sifted through the academic literature for answers on the topic but couldn’t find anything of use.

So, he investigated the data himself. He wanted to find how much retirees could safely spend each year without the well running dry.

He looked at what would happen if someone retired every year since 1926, and what the outcome would be based on different withdrawal rates - the percentage of your retirement savings that you can safely withdraw each year to ensure your money lasts throughout your retirement.

Bengen was aware that the US had seen some torrid stock market downturns, such as the 89% peak to trough fall during the Great Depression, and the 34% decline in 1973-1974. And he knew that these kinds of bear markets could be harmful to retirees, especially if they happened early in retirement (so-called sequence of returns risk).

Bengen wanted a fixed withdrawal rate that could outlast any 30 year period, even the worst ones.

Using a portfolio of 50% US stocks, 50% US bonds, he found that a starting withdrawal rate of 4.15%, with the initial dollar amount adjusted thereafter for inflation, would ensure a retiree wouldn’t run out of money over a 30-year period.

That 4.15% became the ‘4% rule’, and it ended up revolutionizing retirement planning. It became a simple rule that advisors and their clients could use.

It meant retirees could easily calculate how much they needed to save for retirement - by simply dividing the amount of money they would like to spend each year by the withdrawal rate. So if they wanted $50k each year from their portfolio at a 4% withdrawal rate, they could divide $50k by 4%, equalling $1.25 million.

How 4.15% became 4.7%

Critics of Bengen thought his 4% withdrawal rate was too low. But Bengen himself admitted it was very conservative, based on surviving worst-case scenarios.

Like other advisers, Bengen subsequently found that many retirees didn’t spend enough. They’d take their dividends and interest and try not to tap their principal.  That ran counter to the 4% rule though Bengen copped some of the heat anyhow.

In his new book, A Richer Retirement: Supercharging the 4% Rule to Spend More and Enjoy More, Bengen, now retired, has refined his research and come up with fresh strategies to ensure people get the most out of their retirement.

He’s tinkered with the data, and instead of using a 50% equities/50% bonds portfolio as he initially did, he increased the number of assets and created a more diversified portfolio – adding micro, small and midcap stocks in the US as well as international stocks.

Each one of the additions increases the withdrawal rate that retirees can use. Consequently, Bengen has changed his estimate of a safe withdrawal rate from 4.15% to 4.7%.

Again, that’s a conservative number, and Bengen suggests that he’d probably recommend 5.25-5.5% for today’s retirees.

The biggest enemies for retirees

Bengen says inflation is the biggest enemy for retirees. In the 1970s, US inflation averaged 8-9% per annum. It destroyed many retiree portfolios. That period had significant input into his 4% rule.

The other enemy is a bear market, especially a prolonged one. In America, there were two severe bear markets in the first half of the 1970s. Combined with high inflation, retirees were impacted not only by nominal portfolio declines, but it was worse when adjusted for inflation.

Bengen says if you can avoid periods of high inflation or a bear market at the start of retirement, then things should turn out fine (much easier said than done).

The ‘free lunches’ for retirees

Bengen says there are four ‘free lunches’ that can add to your withdrawal rate without adding additional risk:

  1. Diversifying your portfolio
  2. Rebalancing once a year
  3. Slightly tilting your equity allocations to microcap and small cap stocks
  4. A rising equity glide path

The last point needs elaboration. Bengen suggests starting with a lower stock allocation of 30-40%, before increasing it each year.

Bengen says the data indicates that this results in a higher withdrawal rate.

He admits he was surprised by the results, though they make some sense. If you encounter a bear market early in retirement, having low stock exposure will protect you, and when markets rebound, you’ll be buying into that through your rising equity glide strategy.

His other piece of advice is that everyone is different and your retirement portfolio and spending should be customised to suit you.

 

James Gruber is Editor of Firstlinks.

 

10 Comments
Johns
August 14, 2025

I was told 25 years ago how much you needed in savings. The rules then were
At 65 = 13 times annual living expenses
At 60 = 15 times
At 55 = 17 times
Under 55 = 20 times

Again close to the 4% rule. And it makes sense that the older you are when you retire, the shorter your money has to last so the lower the multiple. Obviously assumes you spend your last dollar the day before you die

Dudley
August 14, 2025

"how much you needed in savings" ..."At ...":

Using time to death to better personalise:
https://www.firstlinks.com.au/how-much-do-you-need-to-retire-comfortably

Minimum average net real total return per year required throughout retirement:

https://iili.io/JV1zXJp.png
[ https://freeimage.host/i/image.JV1zXJp ]

Example: Cell C5; with capital 128 times expenses, can lose 1.92% every year until death in 64 years from present.

Increasing Age Pension income 'kicking in' complicates calculations, so table less useful where that occurs - but not irrelevant

John Edwards
August 14, 2025

I’m curious what is a sustainable rate for Australians given our enhanced share market returns from franking, and the tax benefits of super in pension mode?

Wildcat
August 14, 2025

Interestingly we've moved closer to 5% over time although I was aware of the 4% rule. I still regard 5% as a little cautious, especially once the client is over 65 (Nothing to do with the ABP drawdown rates). We found retirees might be limiting their lifestyle or being too cautious about in life giving if that was important to them. Yes we can have a sustained period of low returns but we don't run set and forget strategies for 30 years which the 4/5% rule implies. We review every year and adjust course as required by lifestyle, markets, family needs etc. This allows you to permit higher levels of drawdowns, especially in the early years where travel may be a higher priority, without overly jeopardising the later years. Also simplistically if you earn 5% for income and 2.5% for inflation (yes it's been a bit higher recently) then your total return target is 7.5% as a long term nominal average return. This hasn't represented a challenge over the last 20 years. In fact many of our clients have seen their wealth increase not only in nominal terms but real terms as well. This means they can either live longer than Yoda or start in life giving and still be safe.

Aussie HIFIRE
August 14, 2025

Another factor for Australians is the very generous age pension which provides a risk free $45,000 a year to a couple who own their own home. Between that and say $400,000 in super which would give an income of $60,000 pa with zero tax, likely zero dependents, and zero mortgage to pay which should allow for a very comfortable retirement!

Lisa Romano
August 14, 2025

Bengen's legacy is that he helps us think more clearly about long term market effects as they relate to our own goals, framed within his own extensive research. I often find myself too conservative in withdrawals, aware of the recent impacts of inflation on cost of living, but not taking into account its more positive effect on stock portfolios.

Rob
August 14, 2025

Totally academic to "overlay" the US 4% rule on Australian retirees where 4% is only "possible" ex Superannuation accounts if you are under 65. As a "start" point as to how much you should have in Super at the point of retirement - 25 times your cost of living, ie the inverse of 4%, has merit

Under age 65  4% 
65 – 74  5% 
75 – 79  6% 
80 – 84  7% 
85 – 89  9% 
90 – 94  11% 
95+  14% 

john
August 14, 2025

Just because you have to withdraw more than 5% from super does not mean you have to spend it.

So you could follow a 4% (or 5%) rule in Australia.

JimG
August 14, 2025

Even though there are minimum draw down rates for Super in the pension phase, there is no maximum rate, and there are many ways to effectively go under the minimum rate (by for example recontribution).

Robert Barnes
August 14, 2025

For Australians, tax-free super in retirement makes a significant difference to these calculations.

 

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