Retirement Retirement Planning

MIT Research Says One 401(k) Mistake Costs Couple Thousands in Retirement Savings

Most couples have no idea they're making it.

By Catherine Collins , Edited by Kristy DeSmit

Updated April 1, 2026

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According to research from MIT, couples where both spouses work for an employer that offers a 401(k) match may be leaving money on the table. That's because many couples contribute individually to their own 401(k)s, without creating a joint plan to maximize employer matches. This oversight is more common than people realize and can result in significant lost investment gains over time.

This MIT research analyzed 44 million workers and 6,000 employer-sponsored retirement plans. They referenced this data with IRS tax records to find out whether or not couples communicated about maximizing their retirement benefits. The results were surprising, even to the researchers themselves.

Here are some takeaways from the research and what this mistake can cost couples in the long run.

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Not communicating about 401(k) matches costs couples

The MIT research discovered that 24% of couples did not optimize their retirement contributions based on which spouse earned a higher employer match.

They found that if those couples plan to take advantage of the employer that offered the higher match, they could have increased retirement balances by $750 per year. That, over time, leads to large lifetime investment losses.

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Lifetime losses could be as much as $40,000

Because 401(k) investments grow and benefit from compound interest over a long period of time, the roughly $700 per year in losses could translate to thousands of dollars in lost investment income over the course of a career.

The study found that the average lifetime loss was $14,000 due to these couples forfeiting employer match money, but for 10% of couples, losses could be as much as $40,000.

Many couples are not making these mistakes on purpose

The MIT study also found that many couples were not making these investment mistakes on purpose. In fact, many of them did not understand that coordinating investment allocations and 401(k) contributions could lead to higher earnings over time.

Other couples were worried about asset division in the event of a divorce or preferred to manage their 401(k) plans on their own to maintain a sense of independence.

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These inefficiencies persist after several years

One aspect of the study that surprised researchers was that these issues existed even if a couple worked for the same employer. This showed that for many, it's not a lack of information but rather a failure to communicate and collaborate as a team.

Additionally, the data showed that many couples made this mistake year after year. That means many couples, especially those unaware of their inefficiencies, typically use the same 401(k) contribution strategy every year without updating it.

Increased contribution limits could mean higher losses

As of 2026, the maximum 401(k) contribution limit is now $24,500. Because of this increased contribution limit, individuals have more opportunities to earn money through employer matching, depending on the employer's policy.

If couples are not able to communicate effectively and make a joint plan for how to take advantage of matched contributions, they could sustain higher losses each year.

Communicating helps couples avoid expensive mistakes

The research from MIT shows that couples who were more financially connected with joint accounts, children, and shared homeownership were more likely to coordinate their retirement planning.

Ultimately, the study concluded that having more trust and communication with respect to finances and 401(k) contributions could lead couples to add more money over time to their 401(k) retirement accounts.

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Small changes can lead to positive gains

What's unique about this MIT research is that it doesn't encourage couples to earn more or even invest more than they already do. Rather, the study shows some inefficiencies in couples' money management choices when it comes to maximizing employer matches.

By paying attention to which spouse has the more beneficial retirement matching plan, couples can reallocate their contributions to take advantage of the plan that provides the most benefit overall.

Where to get advice on coordinating 401(k) matches

Couples who need help navigating 401(k) contributions can consult a financial advisor who is a fiduciary.

A financial advisor can help couples maximize their employer matches so the couple as a whole can benefit from the maximum amount of free match income.

Bottom Line

To have a stress-free retirement, couples can work together to maximize their employer benefits. In situations where both partners work and receive an employer match, choosing to maximize the highest match first can help ensure couples don't miss out on investment gains in the future.

As a benefit, this financial decision doesn't require couples to contribute more to their retirement accounts. Rather, couples decide how to re-allocate what they were already contributing in a way that makes the most financial sense for them as a whole.

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