If you’ve opened the Trump Accounts app, the pitch is designed to stick: invest $250 a year and the app shows about $19,000 by age 18 or $878,000 by age 55. Put in the $5,000 annual max and the projection jumps to $271,000 by age 18 and $13 million by age 55. Fortune reports those eye-popping figures come from the government projection on TrumpAccounts.gov, but they rest on an assumption of the S&P 500’s historical annual return of more than 10% sustained without interruption for 55 years.

That “more than 10% for 55 years” is the part financial planners want you to stare at, not skim. Morningstar provided CNBC with data suggesting U.S. stock market returns could be lower over the next decade, closer to an average return of 6.3% per year. And even if you accept a lower long-term return, the math changes dramatically. The deeper point, though, is not just “returns might be lower.” It is that the headline numbers can make parents underestimate what really drives outcomes: time, not deposits.

Trump Accounts are tax-advantaged accounts for children created under President Donald Trump’s tax law, officially launched July 4. They work like a traditional IRA during the “growth period” from birth through the year before a child turns 18, with special rules. Eligible babies born between 2025 and 2028 receive a one-time $1,000 seed deposit from the U.S. Treasury. Families, friends, and others can collectively contribute up to $5,000 per year in after-tax dollars, with the limit indexed for inflation after 2027.

So what could a family actually build using more conservative assumptions, as four financial experts told Fortune? Pam Krueger, a registered investment advisor and founder of Wealthramp, modeled a family that maxes out contributions: add the $1,000 seed to $5,000 a year from birth through age 18, for roughly $91,000 contributed. With a 7% long-term annual return assumption, Krueger projected the account could grow to roughly $185,000 by age 18. Left untouched after that, it could grow to more than $1 million by age 45. Krueger emphasized that time in the market is doing the heavy lifting, pointing to the power of compounding growth.

Mitch Hamer, founder and lead advisor at Intersecting Wealth, echoed the same engine. Using a 7% return for his own 5-year-old son’s account, he projects that maxed annual deposits reach $1 million at age 45 and $3 million at 60. At 8%, which he considers defensible, the figures climb to $1.4 million at 45 and $4.5 million at 60. Hamer notes those totals are built on just $200,000 of contributions by age 45, reinforcing the idea that contributions are almost beside the point. A long time horizon, and no interruption of compounding, is “a powerful concept in personal wealth accumulation,” he told Fortune.

Then comes the catch parents may be least prepared for, and it is not market volatility alone. Matthew Chancey, a certified financial planner, tax strategist, and founder of Tax Alpha Companies, pointed out that of the $1.5 to $2 million he projects a maxed account could reach by age 55 at a 7% return, only about $91,000 is family contributions. The rest comes from time. “That’s not a rounding difference, it’s the whole story,” he said, and the practical implication follows: the only real question is whether the kid can leave the money alone long enough for time to do what time does.

Krueger sharpened the same lesson with percentages: using a 7% assumption, more than 90% of the eventual value comes from decades of compounding, not deposits. But even if time does its job, there are two other issues experts flagged repeatedly. First is taxes and how “tax-deferred” differs from “tax-free.” Unlike a Roth IRA, withdrawals from a Trump Account are taxed as ordinary income, and the account converts to a traditional IRA the day a child turns 18. That means withdrawals before age 59 1/2 can trigger a 10% penalty unless an exception like education or a first-home purchase applies. Second is control at 18. Chancey warned that when the child turns 18, parents go from being in charge to being on the sidelines, “legally, practically, and completely.” He described a pattern families assume they would resist, until a hard year arrives in the kid’s 20s, and then 40 years of tax-free growth can be spent on one temporary problem.

For many parents, the natural question is where Trump Accounts fit with a 401(k) and a 529. Fortune’s financial planners said it is additive, not a replacement. But they did agree on a sequence: maximize an employer 401(k) match first. Chancey called an uncaptured 401(k) match a “free money” opportunity you should not leave on the table, warning that funding a Trump Account before capturing the full match can be an “expensive mistake dressed up as good parenting.” From there, planners generally sequenced a 529 and then the Trump Account. Krueger said a 529 might be prioritized if college is likely because of education tax benefits. Her view: a Trump Account’s biggest advantage is that contributions do not require the child to have earned income, helping “put the dollars where they’ll work the hardest.”

There is also an employer layer now showing up as “free money.” Companies including Uber, Intel, IBM, and Nvidia have pledged to contribute to workers’ Trump Accounts as a benefit. Many employers will add up to $2,500 a year per employee, which counts toward the $5,000 limit.

The strategic stakes for peers who influence personal finance outcomes are clear: the app’s headline projections can be directionally motivating, but they are built on specific market assumptions and can be derailed by the real-world constraints experts keep highlighting. For boards and finance leaders watching how families plan for the future, the takeaway is less about whether $1 million by 45 is possible and more about whether parents will understand what assumptions they are betting on, what taxes they face after age 18, and whether the money can stay invested long enough for compounding to do its job.