Compound Interest Calculator for Kids
Enter how much your child can save, pick a time frame, and see what starting early really means in dollars.
Why Starting Early Changes Everything
Compound interest is the one financial concept that rewards patience more than income. A child saving $5 per week from age 10 with a 7% average return reaches $130,000 by age 65. Wait until 25 to start, and that same $5 per week only reaches $72,000. The child who starts at 10 wins by $58,000. Not because they saved more, but because they started sooner.
That 15-year head start is the entire point of this calculator. When your child can see the number - their specific number, with their savings rate and their timeline - the concept stops being abstract.
How Compound Interest Works
Simple interest pays you based on your original deposit only. Compound interest pays you on your deposit plus all the interest already earned. Year one, you earn interest on $100. Year two, you earn interest on $107. Year three, on $114. The base keeps growing, so the interest payment grows too, even if you never add another dollar.
Add regular contributions and the effect becomes dramatic. Every $5 your child saves today earns interest for the full remaining timeline. A $5 deposit at age 10 is worth $107 at age 65 at 7% - a 21x multiplier from a single week of saving.
The Right Growth Rate to Use
This calculator offers three options. The 2% savings account rate reflects what most bank accounts pay today. The 7% S&P 500 rate is the historical inflation-adjusted average - useful for teaching about investing, but it comes with real-world variability (some years up 30%, some down 20%). For teaching, start with 2% to show basic compounding, then switch to 7% to show the difference investing makes. The contrast is the lesson.
What to Do After the Calculator
Use this number as a conversation starter, not a financial plan. Open a savings account with your child and let them watch the balance grow. Many banks have youth accounts with no fees. For older teens, a custodial investment account can introduce real market investing with small amounts. The goal is building the habit of consistent saving, not hitting an exact number.
This calculator is for educational purposes only. It shows how compound interest works using the growth rate you choose. It is not financial advice.
Frequently Asked Questions
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Compound interest means your money earns money, and then that money earns money too. Start with $100. It earns $7 in a year. Next year, you earn interest on $107, not just $100. That extra $0.49 might seem small, but over 30 years it turns a $100 deposit into over $760. All without adding a single dollar.
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Use the snowball analogy. A tiny snowball rolled down a long hill gets bigger and bigger on its own. The longer the hill, the bigger it gets. Your child's money works the same way. Ask: "Would you rather have $100 today, or $1 that doubles every day for 30 days?" (The doubling penny reaches over $5 million.) The shock is the lesson.
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At a 7% annual rate (the S&P 500 historical average, inflation-adjusted), $5 per week for 10 years grows to about $3,770. You put in $2,600. Interest adds $1,170. At 20 years, that same $5/week reaches roughly $11,200, with $10,600 coming from interest alone. The longer the timeline, the more dramatic the effect.
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Ages 8-10 can grasp the snowball concept. Ages 11-13 can handle the "money earns money" framing with actual numbers. By 14-17, they can understand why starting at 16 instead of 25 can mean hundreds of thousands of dollars difference at retirement. Earlier is always better. The concept scales to any age.
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The S&P 500 has returned about 10% per year on average historically, or roughly 7% when adjusted for inflation. Returns are not guaranteed. Some years are up 30%, some are down 20%. The 7% figure used here is a long-term planning average, not a promise. For education purposes it shows what consistent investing can do over decades.
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