The real cost of waiting, kid edition.
Same monthly contribution, three start ages: birth, age 5, age 10. The dollar gap at age 18 is the compounding cost of waiting. Education only, not advice on whether or how to invest for a child.
Same return applied to all three start ages
Often 18; some states' age of majority is 21
Education only. Returns are assumptions, not predictions. The calculator does not include taxes, fees, or inflation; all three start ages experience the same modeled return so the gap shown is the compounding effect alone.
Starting at birth instead of age 10 produces $60,504 more by age 18, with the same $200 monthly contribution.
- Start at age 0 vs start at age 5: $35,478 more by age 18.
- Start at age 0 vs start at age 10: $60,504 more by age 18.
- Start at age 5 vs start at age 10: $25,026 more by age 18.
The gap is the compounding cost of waiting, given the entered return assumption and contribution. It is not a prediction; it is the deterministic math.
Translate each start-age choice into a number of compounding months.
Months = (handoff age - start age) * 12. Age 0 -> 216 months, age 5 -> 156, age 10 -> 96.
For each month, grow the prior balance and add the monthly contribution. Same return for all three start ages.
New balance = previous * (1 + 7% / 12) + $200 monthly
No taxes, fees, or inflation. The only difference between the columns is how many months the math runs.
The dollar gap between two start ages is the compounding cost of waiting.
Age 0 $86,144 - Age 10 $25,640 = $60,504 cost of waiting
Assumptions
- The same monthly contribution and the same annual return apply to all three start ages.
- No taxes, no fees, no inflation. All three columns experience identical conditions; the gap shown is compounding alone.
- Monthly compounding (contributions added at the end of each month).
- The handoff age default is 18; the calculator allows 15 to 25 for states with different ages of majority.
Limitations
- Real returns are not constant; they vary year to year, and a bad sequence (a drop early on) can change the picture meaningfully.
- The calculator does not model account choice (529, UTMA, brokerage). Tax treatment varies; see the 18th Birthday Reveal calculator on this site for account-specific math.
- No state tax effects.
- The assumed return is the user's input, not a prediction.
- It is not a recommendation to invest a specific dollar amount for a specific child.
- It is not a forecast. The return assumption is a user input, not a prediction of future market performance.
- It is not a comparison of account types. All three columns use the same return; tax differences are not modeled.
- It is not personalized advice. Family situation, risk tolerance, and timing all matter; talk to a CFP for the household-specific call.
Common questions.
Why does starting earlier produce so much more by 18?
Compounding. A dollar invested at birth has 18 years to grow at the assumed return; a dollar invested at age 10 has 8 years. The early-start balance compounds on a larger base for longer, and the gap widens every year. At a 7% gross return, starting at birth produces roughly 3x what starting at age 10 produces with the same monthly contribution.
Does this calculator account for taxes or fees?
No. All three columns experience the same modeled return, so the gap shown is the compounding effect alone. Real-world taxes (kiddie tax on UTMA dividends, for example) and fund expense ratios reduce all three balances; using the same return assumption keeps the comparison clean. The 18th Birthday Reveal calculator on this site models account-specific tax drag.
What if I cannot start at birth?
Start as soon as you can. The dollar gap between starting at age 5 and starting at age 10 is itself usually meaningful (the calculator shows it). Each year of delay narrows the compounding window, so the cost of waiting accelerates the closer you get to the handoff age.
Educational simulation only. Real outcomes depend on actual market returns, taxes, fees, and account choice not modeled here. The return assumption is a user input, not a prediction. ClearMoneySchool does not provide personalized financial or investment advice.