Compound interest
Age 9+Interest that earns interest on itself. Your money grows, and then the growth also grows.
At a glance
Compound interest is interest that earns interest on itself. Every period, the new interest is added to the balance, and the next period's interest is calculated on that bigger balance. Over decades that compounding is what turns small consistent savings into life-changing wealth — and what turns small unpaid debts into crushing burdens.
Example sentence
"Save $10 a month for 10 years and it becomes $1,700 because of compound interest."
Why this matters for kids
Compound interest is the single most underrated concept in personal finance, and the gap between adults who internalised it young and adults who didn't is enormous. A kid who saves $50 a month from age ten to age twenty and never adds another dollar — leaving it in a low-cost index fund averaging 7% real return — ends up with more by retirement than someone who starts at thirty and saves $50 a month their entire career. The math is unintuitive because compounding is exponential, not linear, and our brains are bad at exponential. Conversely, on the debt side: a kid who carries a $1,000 credit card balance at 22% APR will pay $1,400+ in interest if they only make minimums. Same math, different sign. A kid who feels both versions in their bones at age ten — wealth-from-compounding and debt-from-compounding — has a permanent compass for every later financial decision.
How to teach it
Use our compound interest calculator. Start with their current allowance — say $5/week, $260/year — and project 50 years at 7% return. The final number will shock them ($100K+). Then change the start age from 10 to 20 and watch the number drop by half. That visceral comparison is the lesson; you do not need to explain the math, only show it. For older kids, do the same exercise with debt: $1,000 unpaid credit-card balance at 22% APR becomes $7,000+ over 10 years if only minimums are paid. The same chart works for both. Repeat the exercise every year or two with bigger numbers as the kid grows; let them play with the inputs themselves. The kid who has fiddled with a compound-interest calculator a dozen times before turning sixteen will never look at a savings account the same way.
Common misconceptions
- Compound interest matters more for wealthy people. Backwards — compounding amplifies any starting amount. Ten dollars a week from a kid is more than enough to demonstrate the effect over a working lifetime.
- It's the same as regular (simple) interest. Simple interest pays only on the original principal; compound interest pays on principal plus accumulated interest. Over decades the difference is staggering.
- You need a special account to get compound interest. Almost every savings account, money market, CD, and investment vehicle compounds — usually monthly or daily. The mechanic is everywhere; the question is the rate.
Related terms
More for parents
Stay in the loop
We ship new free guides, printables, and the occasional deal — roughly twice a month. No spam, unsubscribe anytime.
Three streams available: 30-day welcome series, biweekly newsletter, and (opt-in) daily blog posts. Pick which you want after signing up. One click to unsubscribe from any.