You and your spouse each have a 401(k) at work, and you both contribute. You both feel good about it, but a quiet problem may be building underneath those steady paycheck deductions.

Researchers at MIT Sloan School of Management studied the retirement savings behavior of millions of American couples, and they found a costly blind spot hiding in plain sight.

Most couples lose an average of $14,000 in retirement wealth over a lifetime because of one mistake they never think to check. For some, that number climbs to $40,000. It has nothing to do with picking the wrong fund or contributing too little.

The 401(k) coordination gap that silently erodes your retirement

Many couples fail to direct their 401(k) contributions toward the spouse with the better employer match.

The research, published in the American Economic Review, was authored by Taha Choukhmane of MIT, Lucas Goodman of the U.S. Treasury, and Cormac O’Dea of Yale University. Their dataset covered 2003 to 2018 and included more than 6,000 employer-sponsored retirement plans covering 44 million eligible workers.

The researchers linked employer plan data to secured IRS tax returns and W-2 forms. This allowed them to see exactly how each spouse allocated contributions and how much free employer money they left behind.

How the $14,000 retirement savings loss adds up over time

Suppose your employer matches dollar-for-dollar up to 5% of your salary, and your spouse’s employer only matches 50 cents per dollar to the same cap. If you split contributions evenly between both accounts, you collect less total match money.

The smarter move is to maximize the more generous match first. Then direct remaining contributions to the second account, and most couples never run this comparison.

Key 401(k) findings from the MIT research

• About 24% of couples failed to coordinate their contributions to prioritize the higher match, according to the MIT Sloan researchers.
• One in five couples could boost their retirement savings by roughly $750 per year just by reallocating existing contributions to the higher-match account, according to the PLANADVISER report on the study.
• The average lifetime loss was $14,000 in forfeited employer match money. For the most unfortunate 10% of couples, losses climbed to $40,000.
• One in four couples could have received an average of $682 more each year through better match coordination, per the original MIT research.
• The median household income among couples in the study was $103,000.

Why do so many couples get 401(k) contributions wrong?

The researchers found that roughly half of the inefficient allocations were accidental. Couples simply did not understand that employer match rates differed or did not think to compare them.

The other half made a deliberate choice to keep finances separate. Trust concerns, independence, and confusion about divorce rules all play a role, according to the study.

Divorce fears create a false barrier

Choukhmane noted that some spouses worry about losing access to money in a partner’s account if the marriage ends. But in most states, retirement assets are divided during divorce, regardless of which spouse made the contributions.

“In case of a divorce, they won’t have access to the assets, and so that’s something where information could really help,” Choukhmane told Planadviser. He said financial advisers can clarify how retirement assets are treated during divorce proceedings.

Even same-employer couples make big 401(k) mistake

One of the more surprising findings: Even couples who worked for the same company failed to optimize.

You might expect shared exposure to the same HR materials to solve the problem. It does not.

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“We thought, ‘Well, if you work for the same employer, then you probably know the incentives,’ but even there we see a failure in coordination,” Choukhmane said in the MIT Sloan summary of the research.

“That was quite surprising to us.”

What the IRS 2026 contribution limits mean for couples

The financial stakes have grown since the study period ended in 2018. For 2026, the IRS raised the 401(k) employee deferral limit to $24,500, up from $23,500 in 2025. Workers aged 50 and older can add $8,000 in catch-up contributions, reaching $32,500 total.

Workers aged 60 through 63 qualify for an enhanced catch-up of $11,250 under the SECURE 2.0 Act. The combined employee-and-employer contribution ceiling is now $72,000.

Why higher 401(k) contribution limits amplify the spouse coordination problem

If your household has $49,000 or more in combined 401(k) contribution room (two spouses under age 50), the question of which account gets funded first matters even more. A mismatch in employer match rates at these levels can mean hundreds of additional dollars lost each year.

The average employer match rate is about 4.6% of salary, according to Vanguard’s How America Saves report.

But match structures differ significantly between employers. Some match dollar-for-dollar up to 6%. Others match 50 cents on the dollar up to 3%. That gap is where couples lose money without realizing it.

A step-by-step approach to fixing this for your household

You do not need a financial planner to run this comparison. Here is how to check whether you and your spouse are optimizing your 401(k) contributions.

Steps that help couples compare and reallocate 401(k) contributions

• Pull both plan summaries: Log into each employer’s benefits portal or call HR. Find the exact match formula: the rate, the cap, and any vesting schedule.
• Calculate each match ceiling: If your employer matches dollar-for-dollar up to 5% on a $90,000 salary, the maximum match is $4,500 per year. Run the same calculation for your spouse.
• Compare and prioritize: Direct contributions first to whichever account has the more generous match. Once that match is maxed, shift contributions to the other account.
• Factor in vesting: If one employer’s match vests immediately and the other requires three years, that affects the real value of each dollar matched. Prioritize the plan where you keep the money sooner.
• Set a calendar reminder: Kate Winget, chief revenue officer at Morgan Stanley at Work, recommends couples schedule money check-ins at least twice per year. Open enrollment season is a natural trigger.

When this strategy may not apply

Not every couple will benefit from reallocating. If both employers offer identical match formulas, there is no advantage to shifting contributions. If one spouse is close to leaving a job and unvested match money would be forfeited, keeping contributions in the other account may make more sense.

Couples with large income disparities should also consider the tax implications of shifting pre-tax contributions between higher and lower earners. A tax professional can help model the trade-offs.

Coordination goes beyond the 401(k)

Choukhmane noted that retirement plan coordination is just one example of a broader pattern, as reported by CNBC. Couples who manage money independently, like financial roommates, tend to miss savings opportunities across the board.

He pointed to another scenario: one spouse carrying credit card debt at 20% to 30% interest while the other has idle cash in a checking account earning nothing. Moving that cash to pay off the debt saves the household real money. But it requires communication and trust.

“That requires a certain level of trust, of coordination, of agreeing on things, of giving up some independence,” Choukhmane told CNBC.

Couples who coordinate well share common traits.

• They shared a joint bank account before getting married, which the researchers view as a proxy for financial integration.
• They had been married longer. The strength of marital commitment correlated with better coordination.
• They owned a home together or shared children. These “entanglement” factors made coordination more likely.
• On the flip side, couples who later divorced showed declining coordination well before the split.

The bigger picture for your retirement planning

This MIT Sloan research won TIAA’s 30th annual Paul A. Samuelson Award, one of the most respected honors in retirement research. The recognition reflects how widespread and underappreciated this problem is.

If you are part of a two-income household, the question is not just “Are we saving enough?” It is “Are we saving in the right place?” That one adjustment, with no change to your total contribution amount, could put thousands of additional dollars into your retirement fund.

Winget recommends tying these financial check-ins to life milestones: a new job, a raise, the birth of a child, or the start of a new benefits year. “Are you both aligned on what’s happening with the contributions that you’re making?” she said. “Are these numbers adding up to what your goals and objectives are?”

The conversation may feel uncomfortable. But at $14,000 in lost retirement wealth, silence is the more expensive option.

Related: Expensive Financial Mistakes that People Make in a Divorce