Compound Interest Calculator
Investment Summary
Input Parameters
Year-by-Year Breakdown
| Year | Start Balance | Contributions | Interest | End Balance |
|---|---|---|---|---|
| 1 | $10,000.00 | $2,400.00 | $801.42 | $13,201.42 |
| 2 | $13,201.42 | $2,400.00 | $1,032.85 | $16,634.27 |
| 3 | $16,634.27 | $2,400.00 | $1,281.01 | $20,315.28 |
| 4 | $20,315.28 | $2,400.00 | $1,547.11 | $24,262.39 |
| 5 | $24,262.39 | $2,400.00 | $1,832.45 | $28,494.83 |
| 6 | $28,494.83 | $2,400.00 | $2,138.41 | $33,033.24 |
| 7 | $33,033.24 | $2,400.00 | $2,466.49 | $37,899.74 |
| 8 | $37,899.74 | $2,400.00 | $2,818.29 | $43,118.03 |
| 9 | $43,118.03 | $2,400.00 | $3,195.52 | $48,713.55 |
| 10 | $48,713.55 | $2,400.00 | $3,600.02 | $54,713.58 |
Starting amount
Additional monthly investment
Expected annual return
Investment duration
How often interest compounds
Final Balance
$54,713.58
Total Contributions
$34,000.00
Total Interest Earned
$20,713.58
Effective Annual Rate
7.23%
APY with compounding
Growth Over Time
| Year | Balance | Contributions |
|---|---|---|
| Year 1 | $13,201.42 | $12,400.00 |
| Year 2 | $16,634.27 | $14,800.00 |
| Year 3 | $20,315.28 | $17,200.00 |
| Year 4 | $24,262.39 | $19,600.00 |
| Year 5 | $28,494.83 | $22,000.00 |
| Year 6 | $33,033.24 | $24,400.00 |
| Year 7 | $37,899.74 | $26,800.00 |
| Year 8 | $43,118.03 | $29,200.00 |
| Year 9 | $48,713.55 | $31,600.00 |
| Year 10 | $54,713.58 | $34,000.00 |
Year-by-Year Breakdown
| Year | Start Balance | Contributions | Interest | End Balance |
|---|---|---|---|---|
| 1 | $10,000.00 | $2,400.00 | $801.42 | $13,201.42 |
| 2 | $13,201.42 | $2,400.00 | $1,032.85 | $16,634.27 |
| 3 | $16,634.27 | $2,400.00 | $1,281.01 | $20,315.28 |
| 4 | $20,315.28 | $2,400.00 | $1,547.11 | $24,262.39 |
| 5 | $24,262.39 | $2,400.00 | $1,832.45 | $28,494.83 |
| 6 | $28,494.83 | $2,400.00 | $2,138.41 | $33,033.24 |
| 7 | $33,033.24 | $2,400.00 | $2,466.49 | $37,899.74 |
| 8 | $37,899.74 | $2,400.00 | $2,818.29 | $43,118.03 |
| 9 | $43,118.03 | $2,400.00 | $3,195.52 | $48,713.55 |
| 10 | $48,713.55 | $2,400.00 | $3,600.02 | $54,713.58 |
Calculator Assumptions
- Interest rate: Assumed constant over entire period; actual returns vary year-to-year
- Contributions: Monthly contributions made at month-end and earn interest from the following period
- Compounding: Interest compounds at selected frequency (more frequent = slightly higher returns)
- Taxes: Not deducted; actual returns depend on account type (tax-deferred, taxable, or tax-free)
- Fees: Not deducted; investment fees reduce actual returns by 0.1-1%+ annually
- Inflation: Not accounted for; real purchasing power will be lower than nominal balance
About the Compound Interest Calculator
The Compound Interest Calculator shows how an investment grows when returns are reinvested and themselves earn returns, the snowball effect Einstein reportedly called the eighth wonder of the world. You enter a starting principal, an annual interest rate, the compounding frequency, and a time horizon, and the tool projects the future value along with how much of that total is your contribution versus accumulated interest. Optionally adding regular contributions reveals how steady deposits accelerate growth dramatically.
The math follows the formula A = P(1 + r/n)^(nt), where P is principal, r is the annual rate, n is the number of compounding periods per year, and t is the number of years. The key insight the calculator makes visible is that compounding frequency matters: monthly compounding outpaces annual compounding at the same nominal rate because interest is credited and starts earning sooner. When you add periodic contributions, the tool layers a future-value-of-an-annuity calculation on top of the base growth.
People use it to plan retirement savings, project the growth of an index fund or savings account, compare investment options at different rates, and understand how starting early beats contributing more later. It is equally useful in reverse thinking, seeing how much a debt balance balloons under compound charges. Pair it with the Simple Interest Calculator to see exactly how much reinvesting earnings changes the outcome over the same period.
A practical tip is to use a realistic, inflation-adjusted rate of return rather than an optimistic headline number, since inflation quietly erodes purchasing power over long horizons. Watch the compounding frequency field closely, daily, monthly, quarterly, and annual produce meaningfully different totals over decades. Remember the result is a projection assuming a constant rate; real markets fluctuate, so treat the figure as a planning guide, not a guarantee.
Frequently asked questions
- What is the compound interest formula?
- The core formula is A = P(1 + r/n)^(nt), where A is the final amount, P is principal, r is the annual rate as a decimal, n is compounding periods per year, and t is the number of years.
- Why does compounding frequency change the result?
- More frequent compounding credits interest sooner, so that interest begins earning its own return earlier. At the same nominal rate, monthly compounding yields more than annual compounding.
- How do regular contributions affect growth?
- Adding periodic deposits layers an annuity on top of the base principal. Because each contribution compounds for the remaining time, consistent deposits can dwarf the starting principal over long horizons.
- How is this different from simple interest?
- Simple interest is calculated only on the original principal, while compound interest is calculated on the principal plus all previously accumulated interest, so compound growth accelerates over time.
Calculate simple interest on loans or investments
Calculate daily compounding interest
Calculate Annual Percentage Yield
Calculate future value of investments
Calculate Compound Annual Growth Rate
Plan how to reach your savings target