Kids Compound Interest Calculator
See how savings snowball when interest earns interest. Enter a starting amount, monthly savings, an interest rate and how many years — then watch the chart grow.
Money after 10 years
$1,621.58
- Money you put in
- $1,300
- Money from interest
- +$321.58
- Interest on interest (compounding)
- +$43.58
Rule of 72: at 4% a year, money doubles in about 18 years.
Assumes interest is added every month (monthly compounding). Real savings interest may be taxed, and investments can lose money. The rates are examples to help you learn.
Guide
Key points
- Compound interest means interest earns interest, so savings snowball.
- The longer the time, the bigger the difference — start early.
- 72 ÷ the interest rate ≈ years for money to double.
Simple vs. compound interest
With simple interest, only the money you put in earns interest. With compound interest, the interest earns interest too — like a snowball that grows faster the more it rolls.
- 10,000 at 10% a year, simple: 11,000 → 12,000 → 13,000 after 3 years
- 10,000 at 10% a year, compound: 11,000 → 12,100 → 13,310 after 3 years
The gap is small at first and keeps growing — which is why starting early is compounding’s superpower.
The Rule of 72
Divide 72 by the yearly interest rate to estimate how many years it takes money to double. At 6%: 72 ÷ 6 ≈ 12 years.
Try this
- Change the time from 10 to 20 years and watch the dark (interest) part of the bars grow.
- Compare saving a little more each month with saving for longer — which grows more?
- With a parent, look up a real kids’ savings account rate and try it.
For parents
The calculator assumes monthly compounding and is meant for learning. Real interest may be taxed, and investments can lose value. Focus on the idea that money left to grow works for you over time.
FAQ
Is compound always better than simple interest?
At the same rate, compound grows more, and the gap widens over time.
Can I really get 7%?
7% is an example of long-term investing. Investments go up and down, so 7% a year isn't guaranteed.
Will my bank pay exactly this?
Real interest may be taxed, so it can be a bit less. This calculator is for learning the idea.