Compound growth happens when earnings remain invested or saved and future growth is calculated on both the original amount and previous earnings. It can work in savings and investments, although investment returns are uncertain.
Simple interest and compound interest
With simple interest, interest is calculated only on the original principal. With compounding, earned interest is added to the balance, so later interest can be calculated on a larger amount. The actual result depends on the rate, compounding frequency, fees, taxes and whether the rate is guaranteed.
A simplified illustration
Imagine $1,000 growing at a hypothetical 5% annual rate, compounded once a year, with no deposits, withdrawals, fees or taxes. After one year the balance would be $1,050. In the second year, 5% would be calculated on $1,050, not just the original $1,000. This is an illustration, not a forecast or promised return.
Time and regular contributions
Starting earlier can give money more time to compound. Regular contributions can also increase the amount exposed to potential growth. However, markets do not deliver a steady annual return, and investments can fall in value.
Do not ignore inflation, fees and taxes
A balance can grow in nominal terms while its purchasing power grows more slowly. Fees reduce the amount that remains invested, and tax treatment varies by country and account type. Consider these factors when comparing products.
Risk is part of the picture
Higher expected returns generally involve higher risk. Cash savings, bonds, shares and other assets have different risk, liquidity and return characteristics. Do not choose an investment based only on a compound-growth illustration.
A quick checklist before you act
- Write down the assumptions and the period covered by each number.
- Check whether important costs, fees, taxes or risks have been left out.
- Test a more cautious scenario, not only the optimistic one.
- Revisit the calculation when your circumstances or the underlying numbers change.
Common mistakes to avoid
- Treating an assumed return as guaranteed.
- Ignoring fees, taxes and inflation.
- Comparing different compounding assumptions as if they were identical.
Key takeaways
- Compounding means returns can generate further returns.
- Time and regular contributions can make a meaningful difference.
- Real-world returns are not fixed and may be negative.
- Account for fees, taxes, inflation and investment risk.
Useful calculators
Editorial note: This is general educational content. Verify local rules, product terms, tax treatment and current figures with relevant official sources. Last updated: November 2026. Please check linked primary sources before relying on this guide.
Further reading and primary sources
Sources are provided as starting points for further research. Some links describe U.S. rules or institutions and should not be treated as legal, tax or regulatory guidance for other countries. Check the relevant authority in your own jurisdiction.