How Compound Interest Works
Compound interest means you earn returns not just on the money you originally put in, but also on the interest that money has already earned. Each compounding period, the interest gets added to your balance, and the next period's interest is calculated on that larger total. Over short periods the effect is small, but over decades it becomes the single biggest driver of long-term investment growth — often dwarfing the amount you actually contributed out of pocket.
Why Compounding Frequency Matters (A Little)
Daily, monthly, quarterly, and annual compounding all produce slightly different results for the same stated annual rate, because more frequent compounding means interest starts earning its own interest sooner. The difference between monthly and annual compounding on a typical investment is usually small — often less than a percentage point of the final balance over many years — but it's still worth matching to how your actual account compounds (most savings accounts and investment funds effectively compound daily or monthly).
The Power of Starting Early — and Staying Consistent
Two people who invest the same total amount of money can end up with very different balances depending on when they invested it. Money contributed early has more time to compound, so it contributes disproportionately to the final total. This is why even small, consistent monthly contributions started early often outperform larger contributions started later. Try changing the "Number of Years" field by just 5–10 years to see how dramatically the future value and interest-earned figures shift.
What This Calculator Doesn't Account For
This tool assumes a constant rate of return, which real markets never deliver — actual returns vary year to year and can be negative in some years even if the long-term average is positive. It also doesn't account for taxes, fees, or inflation. For tax-advantaged accounts like a 401(k) or IRA, taxes may be deferred or avoided; for taxable brokerage accounts, dividends and realized gains are typically taxed along the way, which would reduce the effective growth shown here.