You might assume that building up a retirement nest egg is one of the most challenging things you'll ever have to do. After all, it's not easy to find the money for your retirement savings year after year.

But saving for retirement is really only part of the picture. It's just as important to preserve your IRA or 401(k) throughout retirement so your money doesn't run out on you. This is especially important given the possibility of future Social Security cuts.

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For years, experts have recommended the 4% rule for managing retirement plan withdrawals. This guidance has you withdrawing 4% of your IRA or 401(k) balance your first year of retirement, and then adjusting future withdrawals for inflation.

Following the 4% rule gives your nest egg a very strong chance of lasting for 30 years. Unless you're retiring early, that probably gives you a pretty nice cushion.

But for the 4% rule to work well, certain factors need to be present. And research suggests that 4% may not be an optimal withdrawal rate in 2026.

Here's what needs to happen for the 4% rule to work

For the 4% rule to be successful, the following typically needs to be true:

• You're looking at an average retirement in terms of length.
• Your portfolio is invested pretty evenly between stocks and bonds.
• Bond interest rates are decent.

If any of these factors isn't present, the 4% rule may not work for you. So if, for example, your portfolio consists of 80% bonds and only 20% stocks, a 4% withdrawal rate may not hold up. And if you're retiring at 53, the 4% rule also may not work for you.

Meanwhile, Morningstar analyzes the 4% rule every year based on market conditions. And it says that for the typical person retiring in 2026, the safest starting withdrawal rate is actually 3.9%, not 4%.

You might think that's not even a difference worth bringing up. But depending on the amount of savings you have, it could be significant.

Let's say you're retiring with $500,000. A 3.9% withdrawal rate versus 4% means taking out $19,500 a year instead of $20,000.

But let's say you have $2.5 million saved. In that case, a 3.9% withdrawal rate gives you $97,500 your first of retirement. A 4% withdrawal rate gives you $100,000.

And remember, using this rule, subsequent withdrawals are based on that initial withdrawal. This means your withdrawals get more of a bump in future years if you're starting out with a larger amount -- say, $100,000 instead of $97,500.

Should you limit yourself to a 3.9% withdrawal rate in 2026?

Morningstar's guidance is meant to be conservative so that retirees can lower their risk of running out of money. But their latest report also says that some retirees may be able to withdraw up to 5.7% of their portfolio safely their first year of retirement.

That's why you shouldn't necessarily limit yourself to a 3.9% withdrawal rate in 2026 -- or even 4%. Instead, you should assess your expenses, other sources of income, and portfolio composition to determine what rate of withdrawal makes sense.

Let's say you're eligible for a Social Security benefit that can cover most of your retirement costs. In that case, you may decide to withdraw even less than 3.9% of your portfolio your first year of retirement so you can preserve your nest egg.

Or, if you need more income out of your portfolio and you have a large stock position, you may decide to withdraw 5.2% of your balance your first year, but protect yourself by keeping extra cash on hand outside of your IRA or 401(k). That way, you can take on more risk in your portfolio but turn to your cash reserves if the market tanks.

The point, therefore, is to use the 4% rule, as well as Morningstar's guidance, as a starting point. From there, think about your personal circumstances to decide what approach to take to managing your savings.