Compound Interest Calculator
See how your savings grow with compound interest. Enter an initial deposit, monthly contribution, annual interest rate, and compounding frequency (daily, monthly, quarterly, or annually). Results show your final balance, total contributions, total interest earned, and a year-by-year breakdown table.
Example: $10,000 + $500/Month at 7% for 10 Years
Final Balance
$107,143.85
Total Contributions
$70,000
Interest Earned
$37,143.85
Period
10 years
Starting with $10,000 and contributing $500/month at 7% (monthly compounding) for 10 years grows to approximately $107,143.85. Total contributions are $70,000, with about $37,143.85 from investment growth.
Source: FinCalc server-rendered example using the same formulas as the interactive calculator.
Inputs
Results
Starting with $10,000 and adding $500 monthly at 7.0% for 10 years grows to $107,143.85, including $37,143.85 in earned interest.
Final balance
$107,143.85
Total contributions
$70,000
Initial + monthly
Total interest earned
$37,143.85
Balance growth over time
Year-by-year breakdown
| Year | Start | Contributions | Interest | End balance |
|---|---|---|---|---|
| 2026 | $10,000 | $6,000 | $955.34 | $16,955.34 |
| 2027 | $16,955.34 | $6,000 | $1,458.14 | $24,413.48 |
| 2028 | $24,413.48 | $6,000 | $1,997.29 | $32,410.77 |
| 2029 | $32,410.77 | $6,000 | $2,575.41 | $40,986.18 |
| 2030 | $40,986.18 | $6,000 | $3,195.33 | $50,181.52 |
| 2031 | $50,181.52 | $6,000 | $3,860.06 | $60,041.58 |
| 2032 | $60,041.58 | $6,000 | $4,572.85 | $70,614.43 |
| 2033 | $70,614.43 | $6,000 | $5,337.16 | $81,951.59 |
| 2034 | $81,951.59 | $6,000 | $6,156.72 | $94,108.31 |
| 2035 | $94,108.31 | $6,000 | $7,035.54 | $107,143.85 |
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What's Next?
How Compound Interest Works
Direct answer: contributions dominate early years, but compounding accelerates later years; extending the horizon by 5-10 years can add more growth than increasing short-term contribution amounts.
Source context: long-run equity return datasets (e.g., S&P historical ranges) commonly use nominal return assumptions around 6-10% before inflation for planning scenarios.
Methodology and formulas
- Future value lump sum: FV = PV * (1 + r/m)^(m*t).
- Future value series: FV_contrib = PMT * (((1 + r/m)^(m*t) - 1) / (r/m)).
- Total contributions = initial deposit + (monthly contribution * months).
- Total interest earned = final balance - total contributions.
Compound interest means you earn interest on your existing balance and on previous interest. Each period (day, month, quarter, or year depending on your choice), the rate is applied to the current balance plus any contribution you make. Over time, this creates exponential growth — the longer the horizon and the higher the rate, the more dramatic the effect.
Compounding Frequency
Daily compounding uses 365 periods per year; monthly uses 12; quarterly uses 4; annually uses 1. More frequent compounding yields a slightly higher effective return. Savings accounts often compound daily; many bonds or funds compound monthly or quarterly. This calculator applies the correct growth factor per month for your chosen frequency.
Example
$10,000 initial deposit, $500/month, 7% annual rate, monthly compounding, 10 years: final balance is approximately $98,000. Total contributions (initial + 120 × $500) are $70,000; the rest is interest. Use the calculator above for your own figures and to see the year-by-year table.
Methodology
The calculator steps through each month. Monthly growth factor = (1 + annual rate / periods per year)^(periods per year / 12). Each month: new balance = (balance + monthly contribution) × growth factor. No taxes or fees are included.
Sources
Data and assumptions align with official publications. For verification and current figures:
- U.S. Bureau of Labor Statistics — CPI, wage data, occupational statistics
Frequently asked questions
How much will my money grow with compound interest?
Compound interest grows your balance by applying the interest rate to your existing balance plus new contributions. For example, $10,000 initial deposit plus $500/month at 7% annual rate (monthly compounding) for 10 years yields roughly $98,000 final balance — about $52,000 in total contributions and $36,000 in interest. Use the calculator with your numbers and compounding frequency to see your projection.
What is the difference between daily and monthly compounding?
Daily compounding applies the annual rate in 365 small steps per year; monthly uses 12 steps. The more frequent the compounding, the higher the effective return. For a 7% annual rate over 10 years, daily compounding yields slightly more than monthly (e.g. a few percent more on the final balance). Savings accounts often compound daily; many investments compound monthly or quarterly.
How do I calculate compound interest with regular contributions?
The formula combines the future value of a lump sum (initial deposit × (1 + r)^n) with the future value of an annuity (monthly contribution × (((1 + r)^n − 1) / r)). This calculator does it month by month: each period you add your contribution, then apply the growth factor based on your compounding frequency. Results show final balance, total contributions, total interest, and a year-by-year table.
Does compounding frequency really matter?
Yes, but the effect is modest for typical rates. Going from annual to monthly compounding at 7% over 10 years might add a few percent to your final balance. Daily vs monthly is an even smaller difference. The calculator lets you choose daily, monthly, quarterly, or annual compounding so you can match your account or compare.
How much should I save monthly to reach a goal?
Use the calculator in reverse: try different monthly contribution amounts until the final balance matches your target. For example, to reach $500,000 in 20 years at 7% with $0 initial deposit, you would need to contribute roughly $950/month with monthly compounding. Adjust initial deposit, rate, and years to explore scenarios.
How much will $500 a month grow in 20 years?
At 7% annual return with monthly compounding, $500 per month for 20 years grows to about $260,000. Total contributions are $120,000; investment growth contributes about $140,000. At 8% return, the ending value is roughly $297,000.
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