A 529 plan compounds federal-tax-free if the proceeds go to qualified education. That's the headline. The calculator below turns the headline into a number that fits your contribution and your timeline.
Run a monthly contribution and a return assumption through it. The output is a year-by-year projection — the same engine that powers the Slyce calculator for our spend-to-own users, here repurposed for the standard 529 question. Toggle between scenarios to see what the state deduction and the kiddie-tax avoidance actually add up to.
How a 529 grows
The 529 is a state-sponsored education savings account. You contribute after-tax dollars; growth is federal-tax-free; withdrawals are tax-free if used for qualified education expenses[1][2].
The compounding math matches any other tax-advantaged retirement-style wrapper. Three inputs shape the output:
1. Monthly contribution. The per-month dollar amount you can sustainably deposit. Most state plans accept any amount from $25 up. The calculator above defaults to a $200/month assumption, which is below the gift-tax exclusion at $19K/year and a common starting figure.
2. Time horizon. The years until withdrawal. For tuition planning, that's typically 18 years for a newborn, 12 for a 6-year-old, and so on. SECURE 2.0's Roth IRA rollover provision and the K–12 tuition allowance soften the "what if I started late" worry, but earlier is always better for compounding.
3. Return assumption. The annual percentage return on the underlying investments. The S&P 500's long-run average is roughly 10% before inflation[3]Based on historical returns. Past performance doesn't predict future results.. Most state 529 plans offer age-based portfolios that start aggressive (90%+ equity) and de-risk toward bond-heavy allocations as the beneficiary nears college age. A blended 7% real-return assumption is a reasonable starting place if you want a conservative projection.
Worked numbers
Three concrete projections with the calculator's default assumptions (10% nominal annual return, monthly contributions, 18-year horizon):
- $100/month for 18 years: ~$60,000.
- $200/month for 18 years: ~$120,000.
- $500/month for 18 years: ~$300,000.
- $1,000/month for 18 years: ~$600,000.
These are nominal numbers — not adjusted for tuition inflation. College tuition has historically risen faster than general inflation, so the real purchasing power of $120,000 in 2044 will buy less than $120,000 of 2026 tuition. Plan for this — bake a 5–6% tuition-inflation assumption into your "what does this actually cover" math separately from your "what does this grow to" math.
The 10% long-run average is also exactly that — an average. Sequence-of-returns risk is real, especially in the last 3–5 years before withdrawal. Most state 529 age-based portfolios shift heavily toward bonds in the final stretch precisely to mitigate this.
What a 529 saves vs. a UTMA at the same return
The structural difference between a 529 and a taxable custodial account is how earnings get taxed along the way. The 529 doesn't pay tax on growth. The UTMA does — under the kiddie tax[4][5].
Worked side by side. Assume:
- $200/month contribution.
- 10% return.
- 18-year horizon.
- 1.5% dividend yield (typical for a broad-market index fund).
- Parent in the 24% federal bracket.
529: $120,000 ending balance. $0 federal tax along the way. Tax-free at withdrawal if used for qualified education.
UTMA: $115,000 ending balance — about $5,000 less. The 1.5% dividend yield throws off about $400 of taxable dividends in year 1, growing each year as the balance grows. Below the kiddie-tax floor for the first 6–8 years, the dividends are tax-free. Past that, they're taxed at the parent's 24% rate above the threshold. Capital gains accumulate too — and even if the parent doesn't realize them, the fund's annual capital-gain distributions are taxable.
The $5,000 spread isn't a fortune, but it's real. And it's a function of the dividend yield and the parent's tax bracket — at higher yields or higher tax brackets, the gap widens.
For more on UTMA tax mechanics, see UTMA tax rules and the kiddie tax. For the head-to-head comparison, custodial account vs. 529 plan walks the full trade-off.
The state-tax deduction (often forgotten)
The federal tax break is the headline; the state deduction is the underrated bonus.
Most U.S. states with an income tax give a deduction or credit on contributions to that state's 529 plan. Examples for 2025:
- Indiana — 20% credit up to $1,000/year ($200 cash back on $1,000 contributed).
- New York — deduction up to $5,000 single / $10,000 joint.
- Iowa — deduction up to $4,028 per beneficiary per parent.
- Pennsylvania — deduction up to $19,000 per beneficiary (matches the federal gift exclusion).
- Maryland — deduction up to $2,500 per beneficiary.
- Illinois — deduction up to $10,000 single / $20,000 joint.
A handful of states (Arizona, Kansas, Maine, Minnesota, Missouri, Montana, Pennsylvania) give the deduction even on out-of-state plans — that's rare. Most states only deduct in-state contributions.
The deduction is live cash. A New Yorker contributing $5,000/year and deducting it at a 6.85% state rate saves ~$340/year. Compounded over 18 years that's another piece of the math. Plug your state's rate and your annual contribution into your tax return planning to confirm — Saving for College maintains a state-by-state grid worth bookmarking.
When a 529 isn't the right wrapper
The 529 is the strongest wrapper for school. It's the wrong wrapper if:
- The kid won't go to college (or might not). The 10% non-qualified penalty is the trade-off for the tax break. SECURE 2.0's Roth IRA rollover (up to $35,000 lifetime, 15-year minimum account age) softens this, but doesn't eliminate it.
- You need flexibility on what the money funds. A car at 17, a gap year, a wedding — the UTMA is the wrapper for those. The custodial account guide covers the full account-type map.
- The kid was born 2025–2028 and you haven't yet claimed the Trump Account. The federal $1,000 seed and any employer match is free money you only get once. Trump Account vs 529 walks the head-to-head.
In practice, most parents stack: 529 + UTMA + Trump Account for kids in the eligibility window, plus a custodial Roth IRA later when the kid earns income. The 529 doesn't replace any of those — it's the school-specific layer.
How to use the calculator
The calculator above runs a year-by-year projection on your inputs. Three things to play with:
- Monthly contribution. Slide it up and down to see the diminishing-returns curve flatten. The first $50/month does outsized work because of compounding.
- Time horizon. A newborn (18 years) compounds dramatically more than a 10-year-old (8 years). If you're starting late, push contributions higher to compensate.
- Return assumption. 7% real (after inflation), 10% nominal, or anywhere in between depending on your portfolio mix.
The calculator output is illustrative — it doesn't account for state-specific tax deductions, in-plan expense ratios (most state plans charge 0.10–0.40% in fund fees), or sequence-of-returns variability. Use it for the order-of-magnitude answer, not for a guaranteed projection.
Common misconceptions
"A 529 only pays for college tuition." It also covers room and board (when at least half-time enrolled), books, supplies, computers, internet, K–12 tuition up to $10K/year, registered apprenticeships, and student loan repayment up to $10K lifetime. The 529 statute has been expanded multiple times since 2017.
"529 contributions are deductible federally." They're not. The federal break is on growth and on qualified withdrawals — the deduction is state-only.
"You can only contribute to your home state's 529." You can pick any state's plan. You don't get the in-state deduction unless you live in that state, but the federal benefits are identical across all 50 plans. Utah, Nevada, New York, and Illinois consistently rank among the lowest-cost plans nationally.
"529 funds count against your kid's financial aid." Parent-owned 529s count as parent assets at 5.64% in the FAFSA formula — the lightest treatment available. Grandparent-owned 529s now also count toward the student's untaxed income line under the simplified FAFSA (post-2024). Student-owned 529s count as student assets at 20%, but most 529s aren't structured that way.
Next steps
Run your monthly contribution through the calculator above. The output is the order-of-magnitude number. For the wrapper-comparison side, see custodial account vs. 529 plan. For the kid-with-earned-income case, the custodial Roth IRA option covers the strongest tax wrapper available. For the dollar-cost-averaging mechanics behind monthly contributions, dollar-cost averaging with everyday spending walks the framework.
If your kid was born 2025–2028, the eligibility checker is the right starting place — the Trump Account seed is the highest-leverage piece and there's a deadline.
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Slyce Editorial
Published May 3, 2026 · Updated May 3, 2026