Compound Interest for Kids: How to Make a Child a Millionaire by 65 With $100/Month

The longer the timeline, the more powerful compounding becomes. Nothing on earth has a longer timeline than the day your child is born. Modest contributions made during childhood, given 65 years to grow, produce balances that feel like they shouldn't be possible.

The $100/month from birth scenario

Contribute $100/month from birth to age 18 (total contributed: $21,600). Stop contributing. Let it grow at 8% until age 65. Final balance: about $1,550,000. Your child becomes a millionaire from less than $22K of input, with no further contributions of their own.

Doubling the contribution

$200/month from birth to 18 ($43,200 contributed), then growing at 8% until 65. Final balance: $3.1 million. The leverage on time is so extreme that the contribution amount is almost an afterthought — what matters is the 65-year window.

Three accounts that make this possible

• Custodial Roth IRA: requires earned income (chores, modeling, family business). Tax-free growth forever.
• 529 Plan: state-tax-advantaged college savings; can be partially rolled to a Roth IRA after 15 years.
• UTMA/UGMA brokerage: flexible, no earned-income requirement, but no tax advantages and child legally owns at age of majority.

The teen Roth IRA hack

Once a child earns income (W-2 or 1099) — babysitting, lifeguarding, summer job — they can contribute to a custodial Roth IRA up to either their earned income or the annual limit ($7,000 in 2026), whichever is less. Parents can fund it on their behalf. Every dollar in a Roth at age 16 has 49 years to compound tax-free.

Birthday-money compounding

Every birthday, every holiday, every grandparent gift can be redirected to the child's investment account instead of toys that will be forgotten in a year. $500 a year from age 0–18, growing at 8% to age 65, becomes about $290,000. That's the cost of one wedding's worth of birthday gifts.

Teaching the lesson is the real gift

Show your child the calculator. Show them what their $50 birthday money will be at age 65. Most kids never see the curve until adulthood, by which point they've missed the cheapest decade of contributions. Showing them young creates lifelong savers.

529 plans and the new Roth rollover

529 plans now let you roll up to $35,000 of unused balance into a Roth IRA after 15 years. This makes 529s safer than ever — even if your kid doesn't go to college, the money continues compounding tax-free in a Roth.