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Compound Interest Calculator
See exactly how your money grows. Add monthly contributions, choose daily to annual compounding, and get an inflation-adjusted result with a year-by-year breakdown.
Future balance
$0
Growth over time
| Year | Contributed | Interest | Balance |
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Why this compound interest calculator is different
Most compound interest calculators stop at three inputs and one number. Real savings do not work that way — you get raises, your bank compounds daily rather than yearly, and $1,000,000 in forty years does not buy what $1,000,000 buys today. This tool models all of it.
Contributions that grow
Set an annual increase so your deposits rise with your salary. Almost no free calculator offers this, and it changes the outcome dramatically.
Real daily compounding
Choose daily, monthly, quarterly, semi-annual or annual. Savings accounts and credit cards compound daily — annual-only tools understate both.
Inflation-adjusted answer
See the balance in today’s money alongside the headline number, so the projection stays honest.
Start or end of period
Deposits made at the start of each period earn one extra period of growth. Toggle it and watch the difference.
Year-by-year table
Expand a full schedule of contributions, interest and balance for every single year — not just a final total.
Instant and lightweight
No sign-up, no page reloads, no ad scripts. Results update as you type, and the chart is drawn without any external library.
How to use the compound interest calculator
- Enter your starting amountWhatever is already invested or saved today. If you are starting from zero, leave it at 0 and let contributions do the work.
- Add your regular contributionChoose monthly or yearly. Monthly is the realistic setting for most payroll-driven saving.
- Set a return rate and time horizonAround 7% is a common long-run stock market assumption after inflation-free nominal averaging; a high-yield savings account is usually far lower.
- Open advanced optionsSet compounding frequency, contribution timing, an annual contribution increase, and your inflation assumption.
- Read the split, not just the totalThe bar shows how much of your balance came from your own money versus interest. Over long horizons interest should dominate.
The compound interest formula
For a lump sum with no contributions, compound interest uses:
A = P × (1 + r/n)ntWhere A is the final amount, P is your principal, r is the annual rate as a decimal, n is the number of compounding periods per year and t is the number of years.
When you add regular deposits, a future-value-of-an-annuity term is added on top:
A = P(1 + r/n)nt + PMT × [((1 + r/n)nt − 1) ÷ (r/n)]This calculator goes one step further and simulates each period individually, which is the only accurate way to handle contributions that increase every year or that land at the start of a period rather than the end.
What compound interest actually does to your money
The defining feature of compounding is that it is not linear. Interest earns interest, so the curve bends upward and the final years contribute far more growth than the first ones. This is why time in the market matters more than the exact rate, and why delaying by a decade is so expensive.
- Simple interest pays only on your original principal. $10,000 at 7% simple interest for 30 years reaches $31,000.
- Compound interest pays on principal plus accumulated interest. The same $10,000 at 7% compounded annually reaches roughly $76,000.
- Compounding also works against you on debt. Credit cards compound daily, which is why balances snowball — the same maths that builds wealth builds what you owe.
If you are deciding whether to invest a windfall all at once or spread it out, our guide on dollar-cost averaging versus lump sum investing covers the trade-off. If you are still building a cushion first, start with building an emergency fund.
Which rate should you use?
Savings and cash
Use the account’s stated APY, which already accounts for compounding. Set the compounding frequency to daily for most online savings accounts. A certificate of deposit will quote a fixed APY for its full term.
Long-term investing
A diversified stock index has historically returned somewhere around 7–10% nominal over multi-decade periods, before fees and tax. Many planners model conservatively at 6–7%. Inside a Roth IRA or after capturing a 401(k) match, the effective outcome improves further because growth is sheltered.
Be honest about fees
A 1% annual fee does not cost you 1%. Over thirty years it can quietly remove a fifth or more of your final balance. Subtract fees from your rate before entering it here.
Frequently asked questions
Use A = P(1 + r/n)^(nt), where P is the principal, r is the annual rate as a decimal, n is the number of compounding periods per year and t is the number of years. If you also make regular deposits, add the future value of those deposits on top. This calculator simulates every period individually so contribution increases and start-of-period deposits are handled exactly.
Simple interest is paid only on your original principal, so growth is a straight line. Compound interest is paid on the principal plus all interest already earned, so growth curves upward. At 7% over 30 years, $10,000 grows to about $31,000 with simple interest but roughly $76,000 with annual compounding.
It matters, but less than people expect. Moving from annual to daily compounding at 7% raises the effective annual rate to about 7.25%. Over decades that gap is worth real money, which is why the calculator lets you pick daily, monthly, quarterly, semi-annual or annual rather than assuming one.
Many planners model a diversified stock portfolio at 6–7% nominal to stay conservative, since long-run historical averages sit closer to 7–10% before fees and tax. Cash savings should use the account’s quoted APY instead, which is typically far lower. Always subtract fund fees from whatever rate you enter.
Divide 72 by your annual return rate for a quick estimate. At 8% that is roughly nine years; at 6% it is about twelve. The calculator shows this doubling estimate beneath the growth chart automatically once you enter a rate.
Inflation, yes. Enter your assumed inflation rate in advanced options and the result shows the balance in today’s purchasing power alongside the headline figure. Taxes are not deducted, because the treatment depends entirely on the account. Growth inside a Roth IRA or 401(k) is sheltered, while a standard brokerage account is not.
Yes. Open advanced options and set an annual contribution increase percentage. If you raise your deposits by 3% a year to track pay rises, the final balance can be dramatically higher than a flat contribution over the same period. Most free calculators cannot model this at all.
Run your own numbers
Change one input and watch decades of growth shift in front of you. That is usually the moment saving stops feeling abstract and starts feeling worth doing.
Back to the calculatorResults are estimates for planning and education only, based on a constant rate of return. Real investment returns vary year to year and can be negative. This is not financial advice — check with a qualified professional before making decisions.