This article explains public financial information. It does not recommend buying, selling or holding any investment.
Returns can earn returns
Simple interest applies a rate only to original principal. Compounding adds earned interest or returns to the balance, so later returns apply to a larger base.
The mechanism also works against a borrower when unpaid interest is added to debt. It is a mathematical process, not automatically a benefit.
Understand the formula and its assumptions
A common formula is A = P(1 + r/n)^(nt), where P is principal, r the annual rate, n compounding periods and t years.
Market returns are not fixed. Use several scenarios rather than presenting one projected balance as guaranteed.
Time and contributions drive the base
More time creates more compounding periods. Regular contributions add principal, although their timing changes the outcome.
Starting earlier can help, but no period of market growth is assured and losses can delay recovery.
Fees, inflation and taxes also compound
A recurring fee reduces both the current balance and future returns earned on that balance. Small annual differences can become meaningful over decades.
Inflation reduces purchasing power and taxes depend on account type and jurisdiction. Compare real, after-cost outcomes.
Use the Rule of 72 carefully
Dividing 72 by an annual percentage rate roughly estimates doubling time. At 6%, the estimate is about 12 years.
The shortcut assumes a steady positive rate and ignores volatility, contributions, fees and taxes.
Inputs that change compounded growth
| Input | General effect | Caveat |
|---|---|---|
| Time | More compounding periods | Returns remain uncertain |
| Return | Faster growth | Higher return may mean higher risk |
| Contributions | More principal | Timing matters |
| Fees | Lower ending value | Cost repeats annually |
Frequently asked questions
What is compound interest?
Interest earned on principal plus interest previously added.
How often can it compound?
Daily, monthly, quarterly or annually depending on the product.
What is the Rule of 72?
Divide 72 by a steady annual percentage rate to estimate doubling time.
Is compound growth guaranteed in stocks?
No. Market returns vary and losses occur.
Official sources
Definitions and methodology were checked against these primary resources. Consult the current documents for complete details.
Investor.gov — Compound Interest Calculator ↗Investor.gov — Fees and Expenses ↗
