Parents ask me a version of this question in almost every consultation: “If we contribute $X a year to our kid’s Roth IRA, what will that actually be worth by the time they retire?” It’s a fair question — the numbers involved are large enough, and the time horizon long enough, that intuition alone doesn’t get you there. Below is a calculator that does the math, plus an explanation of what’s happening under the hood.
Quick Answer
A custodial Roth IRA started when a child is young gets 50+ years of tax-free compounding before traditional retirement age. A single $3,000 contribution at age 10, left untouched at a 7% average annual return, is worth roughly $95,000 by age 65 — without another dollar ever being added. Use the calculator below with your own numbers.
Custodial Roth IRA Growth Calculator
This calculator assumes a constant annual return compounded monthly, with no withdrawals, no additional contributions after the period you specify, and no adjustment for taxes, fees, or contribution limits. It’s a planning illustration, not a projection or guarantee.
The Math Behind the Numbers
Two things make a child’s Roth IRA behave so differently from an adult’s:
- Time. Money contributed at age 10 has 55 years to compound before age 65. Money contributed at age 30 has 35. That 20-year gap isn’t a modest edge — at a 7% return, it roughly quadruples the eventual value of the exact same dollar.
- Tax treatment. Because it’s a Roth account, none of that growth is taxed on the way out (assuming qualified withdrawals in retirement). A taxable account growing the same amount would owe capital gains tax along the way, which quietly erodes the compounding.
The formula the calculator above uses is the standard future value of a series of monthly contributions, followed by continued compounding with no further contributions:
then FV65 = FV × (1 + annual rate)^(years remaining to 65)
Sample Scenarios
| Scenario | Total Contributed | Value at 65 (7% avg. return) |
|---|---|---|
| $100/month from age 8–18 (10 yrs) | $12,000 | ~$430,000 |
| $3,000 one time at age 10, never added to | $3,000 | ~$95,000 |
| $250/month from age 14–18 (4 yrs, teen job) | $12,000 | ~$300,000 |
Notice the second row: a single $3,000 contribution at age 10 ends up worth more than a quarter of what ten full years of $100/month produces. Starting early does a meaningful share of the work by itself, before you even factor in how much is contributed.
What the Calculator Doesn’t Account For
- Annual contribution limits. The IRS caps contributions at the lesser of the child’s earned income or the annual limit ($7,500 for 2026) — the calculator won’t stop you from entering an unrealistic monthly figure.
- Market volatility. Real returns don’t arrive as a smooth 7% every year — some years are down 20%, others up 30%. The average may land near historical norms over multiple decades, but the ride is not linear.
- Fees. Using $0-expense-ratio funds (like Fidelity’s ZERO series) or near-zero-fee index funds (Schwab’s SWPPX, Vanguard’s VTI) keeps more of that growth compounding instead of leaking to fund costs.
For the account-opening side of this — where to actually put the money — see our reviews of the Fidelity custodial Roth IRA, the Schwab custodial Roth IRA, and the Vanguard custodial Roth IRA, or our full ranked comparison of custodial Roth IRA providers.
Frequently Asked Questions
Is this calculator accurate?
It correctly applies the standard compound-interest formula, but any projection is only as good as its assumed return — real markets don’t move in a straight line. Treat the output as an illustration of how time and contributions interact, not a guarantee.
What return rate should I use?
7% is a commonly used long-run average for a diversified stock index portfolio after inflation is roughly netted out against nominal historical returns; many planners use figures between 6% and 8% for multi-decade projections. Lower it if you want a more conservative estimate.
Does the calculator account for taxes?
No — and for a Roth IRA held to retirement with qualified withdrawals, that’s actually the right assumption, since qualified Roth withdrawals aren’t taxed. That tax-free growth is precisely what makes the long time horizon so powerful for a child’s account.
If your child is old enough to be curious about how the number in the calculator actually gets there, The Little Book of Common Sense Investing by John Bogle is a short, plain-language read on why time and low costs matter more than picking the “right” stock.
The Little Book of Common Sense Investing by John Bogle
I reference this when explaining to my kids why starting their Roth IRA early matters more than the amount they contribute.
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