Building a million-dollar 401(k) has become more achievable than ever.

In 2024, the number of Fidelity-managed 401(k) accounts with seven-figure balances grew to 537,000, a 27% increase from the year before, according to data shared with CNBC Make It. Fidelity is one of the largest retirement plan providers in the U.S., overseeing approximately 24 million 401(k) accounts.

This growth was driven by strong stock market performance, with the S&P 500 rising 23% during the year. But it's not just market gains fueling higher balances — consistent contributions, employer matches and the power of compounding have helped long-term investors accumulate more wealth. Fidelity data shows that participants who stayed in the same plan for 15 years had an average balance of more than $500,000.

Even if your account isn't worth seven figures, saving in a workplace retirement plan can help build long-term wealth. About 60% of Americans have a 401(k)-type account and among Fidelity participants, the average balance was $131,700 at the end of 2024.

Starting early can make a big difference. Compounding allows even small contributions to grow exponentially over time and employer matches can accelerate savings. While the total balance needed for retirement varies by individual needs, consistently setting aside a portion of income can significantly increase financial security in retirement.

Are you on track to hit $1 million?

CNBC Make It's compound interest calculator can help you estimate how much your savings will be worth in the future based on factors such as your current balance, savings rate and anticipated rate of return.

After inputting your information below, you can adjust each factor to see how changes in savings or market performance might impact your retirement balance. The tool doesn't automatically include employer matches, so be sure to add them to your monthly contributions for a more accurate estimate.

If the calculator doesn't work for you, try it here.

If you don't have access to a 401(k)-type account through your job, there are other ways to start saving for retirement:

• Individual retirement accounts (IRAs): Like a 401(k), a traditional or Roth IRA comes with tax advantages. Traditional IRAs let you contribute pre-tax dollars, which can lower your taxable income now, while Roth IRAs are funded with after-tax dollars but allow for tax-free withdrawals in retirement.
• Brokerage accounts: While these don't offer the tax advantages of a 401(k) or IRA, they still allow your money to grow through compounding. Plus, they offer more flexibility when it comes to accessing funds, without early withdrawal penalties or contribution limits.

Even small contributions add up, especially with compounding. The key is to save consistently over decades to maximize wealth.

One way to stay on track is by automating monthly contributions from your checking account — 15% of your income is ideal, but even a smaller amount is a good start, especially earlier in life. Plus, with automatic payments, you won't forget to save or be tempted to spend the money elsewhere.

The material and tools displayed on this website are provided without any guarantees, conditions or warranties as to their accuracy.

Disclosure: This calculator was originally created by Kiersten Schmidt for Grow, which is produced by CNBC in partnership with Acorns and is editorially independent.

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