Compound Interest Calculator
Project your investment growth with daily, monthly, or annual compounding — and see the real impact of time and contributions.
Interactive Compound Interest Calculator
Result
Use this free compound interest calculator to project how an investment grows over time. Model lump sums, recurring contributions, daily or annual compounding, and inflation — and see both the nominal balance and the purchasing power in today’s dollars.
How to use this compound interest calculator
Enter your starting balance, expected annual return, and time horizon. Toggle contributions on if you are saving monthly, and add inflation if you want to see real purchasing power. The chart and year-by-year table update instantly.
Common scenarios to try:
- Starting from zero: enter $0 principal and $500/month contributions over 30 years at 7%
- Maximizing a Roth IRA: $7,000/year for 35 years at 8% projected return
- Comparing lump sum vs. DCA: $100,000 now vs. $10,000/year for 10 years
Worked example: $200/month for 40 years at 7%
You start at age 25 with $0 and invest $200/month in a diversified index fund returning 7% annually. By age 65:
- Total contributions: $96,000
- Final balance: $525,000+
- Interest earned: $429,000+
Wait until age 35 to start the same $200/month habit, and the final balance drops to roughly $227,000 — less than half. That single decade of starting earlier adds nearly $300,000 to the result. Time matters more than the rate.
The real story is inflation-adjusted
A 7% nominal return with 3% inflation produces a 4% real return. Over 40 years, that distinction is enormous:
- $200/month at 7% nominal: $525,000 nominal, but only $148,000 in today’s dollars
- $200/month at 4% real: $237,000 (same purchasing power as the $525,000 nominal, but more useful for planning)
The calculator’s inflation-adjusted output reveals what your future balance actually buys.
Compounding frequency: small effect, real dollars
Daily compounding beats annual compounding by about 2% over 30 years on a $10,000 lump sum at 7%. That sounds small, but it is $1,960 in extra dollars on a $76,000 final balance. The real driver is time and contribution consistency — frequency of compounding is a rounding error in comparison.
Tips for accurate projections
- Use real expected returns, not best-case. A diversified equity portfolio has averaged 7-10% nominally, but planning at the higher end leaves no margin for bear markets, sequence-of-returns risk, or extended unemployment.
- Subtract fees. A 0.5% expense ratio on a $100,000 balance costs $500/year — over 30 years, that compounds to six figures of lost return.
- Reinvest dividends. Most calculators assume reinvestment by default. If you are taking dividends as cash, the actual growth is materially lower.
- Account for tax drag in taxable accounts. Dividend taxes and capital gains can subtract 1-2% per year from your net return.
- Plan in real terms. Decide what you want the retirement balance to buy in today’s dollars, then work backward.
Common mistakes
- Assuming historical returns. Past returns do not guarantee future performance, especially over a short sample. Use ranges and stress-test your plan against lower returns.
- Ignoring sequence-of-returns risk. The order of returns matters for retirees drawing down portfolios. A bear market in the first five years of retirement is far worse than one in year 20.
- Stopping contributions during market downturns. The biggest gains come from buying during low periods. Maintaining contributions through volatility is a structural advantage.
- Forgetting about required minimum distributions. Traditional IRAs and 401(k)s require withdrawals starting at age 73, which can push retirees into higher tax brackets.
Related Tools
- Retirement Calculator – Estimate the nest egg you need based on desired retirement income.
- Compound Interest for Small Business – Model business cash reserves growth with regular deposits.
- Inflation Calculator – Convert historical dollars to today’s purchasing power and back.
- Net Worth Calculator – See how compounding savings contribute to overall net worth.
- ROI Calculator – Measure return on investment for one-time purchases or projects.
| Compounding frequency | After 10 years | After 20 years | After 30 years | Difference vs. annual |
|---|---|---|---|---|
| Annual | $19,672 | $38,697 | $76,123 | baseline |
| Quarterly | $19,788 | $39,161 | $77,395 | +$1,272 (30y) |
| Monthly | $19,838 | $39,341 | $77,902 | +$1,779 (30y) |
| Daily | $19,852 | $39,402 | $78,083 | +$1,960 (30y) |
| Continuous | $19,855 | $39,411 | $78,113 | +$1,990 (30y) |
Compare your options
Two methods, three minutes. The honest trade-off table.
This compound interest calculator
- + Daily, monthly, quarterly, and annual compounding options.
- + Inflation adjustment shows purchasing power, not just nominal balance.
- + Run with regular contributions or a lump sum.
- − Cannot model variable returns or sequence-of-returns risk.
Brokerage firm's projection tool
- + Uses historical return data and Monte Carlo simulation.
- + Accounts for fees and expense ratios automatically.
- − Often optimistic by default, with no inflation adjustment.
- − Requires an account and is tied to that firm's products.
Excel or Google Sheets
- + Full control over formulas, contributions, and time periods.
- + Easy to model irregular contributions and withdrawals.
- − No visual chart unless you build one.
- − Formula errors compound over multi-decade horizons.
Who actually uses Compound Interest Calculator?
Five concrete situations pulled from real sessions, with the exact inputs people paste in.
Understand how $200/month grows over 30 years.
Set monthly contributions, pick a reasonable return, and watch the balance grow on the chart. The tool makes compounding concrete — it's not just a number, it's a 30-year trajectory.
See the difference between tax-free and tax-deferred growth.
Run both account types with the same contribution and time horizon. The tool's after-tax output shows which structure ends up with more spendable retirement income.
Figure out how much to save monthly to hit a 2035 tuition goal.
Enter the target amount, the years remaining, and a realistic return. The tool solves for the monthly contribution needed — and shows what happens if you start earlier or later.
Estimate how long a nest egg lasts given withdrawals and continued growth.
Set a starting balance, expected return, and annual withdrawal. The chart shows the year-by-year balance, highlighting the moment compounding turns from friend to opponent.
Compare after-tax returns on identical gross yields.
Run the calculator with the gross return in a tax-advantaged account, then in a taxable account with dividend taxes and capital gains drag factored in.
A compound interest calculator that shows the real impact of time, not just rate
The power of compounding is not the rate — it's the time. A 25-year-old investing $200/month at 7% accumulates more by age 65 than a 35-year-old investing $400/month at the same rate. This tool makes that dynamic visible with a chart, a year-by-year table, and an inflation-adjusted view that reflects purchasing power, not nominal balance.
Chart, table, and inflation-adjusted view in one screen
See the balance curve, the year-by-year breakdown, and what the balance is worth in today's dollars. The three views together explain compounding better than any single number.
Lump sum, monthly contributions, or both
Start with a $10,000 balance, add $500/month, compound daily. The tool handles arbitrary combinations of starting principal, recurring contributions, and compounding frequency.
Inflation adjustment is built in
Toggle on inflation to see the real purchasing power of your projected balance. Without this, you are overstating your future wealth by a factor of 2-3x over a 30-year horizon.
No optimistic return assumptions baked in
The calculator uses whatever return you input. Default to 7% for a diversified equity portfolio, 4-5% for conservative allocations, or run multiple scenarios to see the range.
What you only get here: a compound interest tool with both nominal and inflation-adjusted views, flexible contribution patterns, and a chart that makes 30-year growth tangible.