Compound Interest Calculator
See how savings or an investment grow with compound interest. Choose how often interest compounds, add regular contributions, and follow the balance year by year.
- Daily to annual compounding
- Regular contributions
- Year-by-year growth chart
Investment details
Plan your growth
Live results
Final balance
$31,998.32
Total contributions
$12,000.00
Total interest
$9,998.32
Initial amount $10,000.00 · Effective annual rate 5.116%
Growth over time
Year-by-year growth
| Year | Contributions | Interest | Total interest | Balance |
|---|---|---|---|---|
| 1 | $1,200.00 | $539.50 | $539.50 | $11,739.50 |
| 2 | $1,200.00 | $628.50 | $1,168.01 | $13,568.01 |
| 3 | $1,200.00 | $722.05 | $1,890.06 | $15,490.06 |
| 4 | $1,200.00 | $820.39 | $2,710.44 | $17,510.44 |
| 5 | $1,200.00 | $923.75 | $3,634.20 | $19,634.20 |
| 6 | $1,200.00 | $1,032.41 | $4,666.60 | $21,866.60 |
| 7 | $1,200.00 | $1,146.62 | $5,813.23 | $24,213.23 |
| 8 | $1,200.00 | $1,266.68 | $7,079.91 | $26,679.91 |
| 9 | $1,200.00 | $1,392.88 | $8,472.79 | $29,272.79 |
| 10 | $1,200.00 | $1,525.54 | $9,998.32 | $31,998.32 |
How it works
How to Use the Calculator
- 1
Enter the starting amount
Type your initial deposit. It can be 0 if you are only making regular contributions.
- 2
Set the rate and time
Enter the annual interest rate and the number of whole years, then pick how often interest compounds.
- 3
Add contributions (optional)
Enter a regular amount, choose monthly or yearly, and whether it is added at the start or end of each period.
- 4
Review the growth
Read the final balance, total contributions and total interest, then scan the chart and the year-by-year table.
The Compound Interest Formula
- A: final balance
- P: starting amount
- r: annual interest rate as a decimal (5% → 0.05)
- n: compounding periods per year (1, 2, 4, 12 or 365)
- t: number of years
With regular contributions, each deposit compounds from the date it is added. The calculator steps through every contribution period using the equivalent periodic rate (1 + r/n)n/c − 1, so the results match the closed-form future-value-of-annuity formulas. The effective annual rate shown is (1 + r/n)n − 1.
Worked Examples
Lump sum
10,000 at 5% compounded monthly for 10 years
16,470.09
6,470.09 interest
Monthly saving
100 a month (end of month) at 5% compounded monthly for 10 years
15,528.23
12,000 contributed, 3,528.23 interest
Yearly saving
1,000 at the start of each year at 10% compounded annually for 3 years
3,641.00
3,000 contributed, 641 interest
Common Use Cases
Savings goals
Estimate how long regular deposits take to reach a target balance.
Retirement planning
See how monthly contributions over decades add up, and how much of the total is interest.
Comparing accounts
Compare offers with different rates or compounding frequencies using the effective annual rate.
Business reserves
Project the growth of cash held in an interest-bearing account.
Frequently Asked Questions
What is compound interest?
Compound interest is interest earned on both your original deposit and on the interest already added to it. Because each period's interest becomes part of the balance, growth speeds up over time, unlike simple interest, which is only ever paid on the original amount.
What is the compound interest formula?
Without contributions, A = P(1 + r/n)^(n·t), where P is the starting amount, r the annual rate as a decimal, n the number of compounding periods per year and t the number of years. For example, 10,000 at 5% compounded monthly for 10 years grows to about 16,470.09.
How much difference does the compounding frequency make?
More frequent compounding gives a slightly higher return at the same nominal rate. At 5%, annual compounding gives an effective annual rate of 5%, monthly gives about 5.116% and daily about 5.127%. The calculator shows the effective annual rate for the frequency you choose.
What is the difference between contributions at the start and end of a period?
A contribution at the start of a month or year earns interest for that whole period, while one at the end starts earning from the next period. Start-of-period contributions therefore end with a slightly higher balance.
How are contributions handled when they don't match the compounding frequency?
The calculator converts the annual rate into the equivalent rate per contribution period, i = (1 + r/n)^(n/c) − 1, where c is 12 for monthly or 1 for yearly contributions. This keeps the growth of the starting amount exactly equal to the standard formula.
Does the calculator account for taxes, fees or inflation?
No. Results assume a constant rate with no taxes, fees, withdrawals or inflation adjustment. Real investment returns vary from year to year, so treat the figures as an estimate rather than a guarantee.
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