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Compound Interest CalculatorCompound interest calculator: project your savings growth
Enter an initial investment, a monthly contribution, and an assumed nominal annual rate. Compare how your deposits and compounding affect the balance over time. The chart, annual table, and formula use the same assumptions.
Projected value
$691,150
after 30 years at 7% (monthly compounding)
Total invested
$190,000
Interest earned
$501,150
Year-by-year breakdown
| Year | Contributions | Interest | Balance |
|---|---|---|---|
| 1 | $6,000 | $919 | $16,919 |
| 2 | $6,000 | $1,419 | $24,339 |
| 3 | $6,000 | $1,956 | $32,294 |
| 4 | $6,000 | $2,531 | $40,825 |
| 5 | $6,000 | $3,148 | $49,973 |
| 6 | $6,000 | $3,809 | $59,782 |
| 7 | $6,000 | $4,518 | $70,299 |
| 8 | $6,000 | $5,278 | $81,578 |
| 9 | $6,000 | $6,094 | $93,671 |
| 10 | $6,000 | $6,968 | $106,639 |
| 11 | $6,000 | $7,905 | $120,544 |
| 12 | $6,000 | $8,910 | $135,455 |
| 13 | $6,000 | $9,988 | $151,443 |
| 14 | $6,000 | $11,144 | $168,587 |
| 15 | $6,000 | $12,383 | $186,971 |
| 16 | $6,000 | $13,712 | $206,683 |
| 17 | $6,000 | $15,137 | $227,820 |
| 18 | $6,000 | $16,665 | $250,486 |
| 19 | $6,000 | $18,304 | $274,790 |
| 20 | $6,000 | $20,061 | $300,851 |
| 21 | $6,000 | $21,945 | $328,796 |
| 22 | $6,000 | $23,965 | $358,760 |
| 23 | $6,000 | $26,131 | $390,892 |
| 24 | $6,000 | $28,454 | $425,345 |
| 25 | $6,000 | $30,945 | $462,290 |
| 26 | $6,000 | $33,615 | $501,905 |
| 27 | $6,000 | $36,479 | $544,384 |
| 28 | $6,000 | $39,550 | $589,934 |
| 29 | $6,000 | $42,843 | $638,777 |
| 30 | $6,000 | $46,374 | $691,150 |
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Open calculatorHow to use
- 1
Enter your starting amount in "Initial investment" — use 0 if you are starting from scratch.
- 2
Set "Monthly contribution" to what you can invest every month; it compounds at the exact monthly equivalent of your annual rate.
- 3
Pick an annual interest rate and how many years the money will grow.
- 4
Choose the compounding frequency, then read your projected value — expand "Year-by-year breakdown" to see each year's interest.
- 5
Copy the link to save your scenario, or nudge the rate to compare conservative vs. optimistic outcomes.
Benefits
See compounding visually
The chart shows the exact year your interest starts outgrowing your contributions — the moment saving early pays off.
Compare scenarios in seconds
Change the rate or monthly amount and watch decades of difference appear instantly, no spreadsheet needed.
Learn the real math
The exact formula sits under the tool with a worked example, so you understand what the numbers mean, not just what they are.
Honest monthly math
Monthly deposits use the equivalent monthly rate for your selected nominal rate and compounding frequency.
Compounding Frequency Comparison
Based on $10,000 initial + $500/mo at 7% for 30 yrs
How often interest is calculated determines how fast your earnings start generating their own returns. Notice how the leap from annual to monthly compounding produces a significant jump in wealth, whereas moving from daily to continuous compounding adds only pennies.
| Frequency | Periods / Year | Effective APY | Interest Earned | Projected Value |
|---|---|---|---|---|
Annually | 1 | 7.000% | $470,849 | $660,849 |
Semi-Annually | 2 | 7.122% | $486,872 | $676,872 |
Quarterly | 4 | 7.186% | $495,332 | $685,332 |
MonthlySelected | 12 | 7.229% | $501,150 | $691,150 |
Daily | 365 | 7.250% | $504,017 | $694,017 |
Continuously | ∞ (Infinite) | 7.251% | $504,115 | $694,115 |
Compound Interest vs. Simple Interest
Both projections include the same monthly deposits. Simple interest earns on the money you deposit without earning interest on past interest. Compound interest also earns on accumulated interest.
Simple Interest Payout
Interest on your $10,000 starting balance and each monthly deposit for its time invested, without interest reinvestment.
Compound Interest Payout
Your interest is reinvested every monthly cycle, earning secondary and tertiary interest continuously.
$291,675 higher modeled balance vs. simple interest
Under these inputs, the compound-interest calculation ends $291,675 above the simple-interest comparison after 30 years.
How this compound interest projection works
Compound interest adds earned interest to the balance, so later interest can be calculated on both the principal and accumulated interest. This calculator also adds your monthly contribution at each month-end and applies the selected nominal rate and compounding frequency.
Rate and frequency
The rate is an assumption, not an expected or guaranteed investment return. Monthly deposits use the equivalent monthly rate for the selected frequency; a nominal rate and effective annual yield are different quantities.
What is outside the model
The projection uses a steady rate and does not deduct taxes or fees, adjust for inflation, or model market losses and changing returns. Compare multiple assumptions and use the separate inflation calculator if you want a constant-rate purchasing-power scenario.
How it works
- A
- Future value — what your money grows into
- P
- Initial principal — your starting investment
- PMT
- Monthly contribution — added at the end of each month
- r
- Annual interest rate, as a decimal (7% = 0.07)
- n
- Compounding periods per year (12, 4, or 1)
- rm
- Monthly rate equivalent for the selected compounding frequency
- t
- Number of years
Monthly contributions are added at the end of each month. The rate you enter is a nominal annual rate. With monthly compounding, the monthly rate is the annual rate divided by 12: a 7% nominal annual rate compounds to about 7.23% over a full year. For other compounding frequencies, the calculator uses the equivalent monthly rate (1 + r/n)^(n/12) - 1, where r is the nominal annual rate as a decimal and n is the number of compounding periods per year. This keeps monthly contributions consistent with your selected frequency.
Worked example
$10,000 invested at 7% compounded annually for 10 years grows to $19,671.51 — with no further contributions. Add $500 every month (compounded monthly) and the same 10 years ends at $106,639.02, of which $70,000 is money you put in and the rest is compounding at work.
Understanding your results
The ending balance combines your starting amount, any recurring deposits, and modeled interest. The contribution total shows money you added; the difference is projected growth under the selected rate and compounding schedule. Changing the assumed return changes the estimate, not a guaranteed outcome.
Sources and methodology
These resources explain related concepts. They do not certify or endorse this calculator. See the assumptions and worked example above.
- Compound Interest Calculator — Investor.gov / U.S. SEC ↗
An independent educational calculator for exploring contributions, rates, and compounding.
Frequently asked questions
Compound interest is interest calculated on your original principal plus interest you have already earned. Each compounding period your balance grows a little, and the next period’s interest is calculated on that larger balance. Over long periods this snowball effect does most of the work — which is why time matters more than timing.
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Open calculatorFigures are estimates for education only — not financial advice. Results depend on the assumptions you enter. Read the full disclaimer.