See exactly how your savings grow year by year when interest compounds — with a full yearly breakdown table.
| Year | Deposits this year | Interest this year | End-of-year balance |
|---|
Compound interest means your interest starts earning its own interest. Each period, the bank (or the market) pays interest not just on what you originally put in, but on every dollar of interest that has already accumulated. In the early years the effect looks small, but the curve gets steeper the longer money is left untouched — which is why starting early usually matters more than the exact rate you earn.
The breakdown table shows exactly how much of each year's growth comes from your own deposits versus interest. Early on, deposits usually make up most of the balance growth. Later, interest can end up contributing more per year than your contributions do — that crossover point is often called the moment compounding "takes over."
This tool assumes a constant interest rate for the entire period and doesn't factor in taxes on interest income, investment fees, or inflation eating into real purchasing power. Treat the result as a useful estimate for planning, not a guaranteed outcome.
Enter your starting principal, the annual interest rate you expect, how often interest compounds (annually, monthly, or daily, depending on the account or investment type), and how many years you plan to let it grow. Optionally add a monthly contribution if you plan to keep adding to the balance over time. Click Calculate to see your final balance, total interest earned, and a full year-by-year table showing how the balance builds.
The same annual interest rate produces slightly different results depending on how often it compounds. Interest that compounds monthly earns marginally more over a year than interest compounding annually, because each month's interest starts earning its own interest sooner rather than waiting for the full year to pass. The difference is usually small for typical savings rates but becomes more noticeable at higher rates or over many years — which is why comparing two accounts with the same advertised rate but different compounding frequency isn't quite an apples-to-apples comparison unless you run the actual numbers.
Simple interest is calculated only on the original principal for the entire period, so it grows at a constant, linear rate every year. Compound interest, by contrast, is calculated on the principal plus all previously accumulated interest, which means the growth rate accelerates over time rather than staying flat. Over short periods the difference between the two is small, but over 10, 20, or 30 years, compound interest can produce a dramatically larger final balance than simple interest at the same stated rate — which is exactly why almost all savings accounts, investments, and loans in practice use compound interest rather than simple interest.
Because compound growth accelerates over time, money invested earlier has significantly more time to benefit from compounding than the same amount invested later — even if the later investment is larger. A classic illustration: someone who invests a modest amount starting in their 20s and stops contributing after 10 years can end up with a similar or larger balance at retirement than someone who starts investing a decade later and contributes for twice as long, purely because of the extra years of compounding on the early contributions. This is the core reason financial advisors consistently emphasize starting to save and invest as early as possible, even in small amounts.
Does this calculator account for taxes on interest earned? No — interest and investment gains are often taxable depending on the account type (a regular brokerage account vs. a tax-advantaged retirement account, for example). Consult a tax professional for guidance specific to your situation.
Why does my bank's compound interest result look slightly different? Small differences often come from exact compounding schedules, how deposits are timed within each period, or rounding conventions — this calculator provides a standard estimate using the compound interest formula.
Is a higher compounding frequency always significantly better? The difference between monthly and daily compounding at the same rate is usually quite small in practice — the interest rate itself and the length of time invested matter far more than compounding frequency alone.
What's a realistic annual return to use for long-term projections? This varies widely by investment type — savings accounts, bonds, and diversified stock portfolios all have very different typical long-term returns. Using a conservative, well-researched estimate for your specific investment type gives a more reliable projection than an optimistic guess.
Can I model irregular contributions with this calculator? This tool assumes a consistent monthly contribution amount throughout the period — for irregular contributions, running the calculation in separate segments for each contribution pattern gives a closer approximation.
Does this calculator work for calculating loan interest instead of savings growth? The compounding math is mathematically similar, though a dedicated loan or mortgage calculator is generally better suited for loans, since it also accounts for amortization and fixed payment schedules that this savings-focused tool doesn't model.
What's a reasonable way to pick an interest rate assumption for this calculator? Base it on the actual account or investment type you're modeling — savings account rates, CD rates, and long-term market averages differ substantially, so using a figure specific to your situation gives a far more useful projection than a generic guess.
Can I use this calculator to plan for a specific savings goal? Yes — adjust the monthly contribution and time period until the projected final balance matches your target, which gives a practical sense of what it takes to reach a specific savings goal.
Last reviewed by Mehmed on July 11, 2026.