Compound Interest Calculator
Growth with monthly contributionsRuns locally · nothing uploaded
Future value
171,752.37
Total contributions
130,000
Total interest
41,752.37
Year-by-year breakdown
| Year | Total contributions | Total interest | End balance | |
|---|---|---|---|---|
| Year 1 | 22,000 | 790.47 | 22,790.47 | |
| Year 2 | 34,000 | 2,235.33 | 36,235.33 | |
| Year 3 | 46,000 | 4,368.06 | 50,368.06 | |
| Year 4 | 58,000 | 7,223.84 | 65,223.84 | |
| Year 5 | 70,000 | 10,839.67 | 80,839.67 | |
| Year 6 | 82,000 | 15,254.44 | 97,254.44 | |
| Year 7 | 94,000 | 20,509.01 | 114,509.01 | |
| Year 8 | 106,000 | 26,646.37 | 132,646.37 | |
| Year 9 | 118,000 | 33,711.66 | 151,711.66 | |
| Year 10 | 130,000 | 41,752.37 | 171,752.37 |
Results are estimates for reference only and are not financial, lending or tax advice. Confirm actual rates and taxes with your lender or tax authority.
How it works
When to use it
- Project how a lump sum grows at a fixed annual rate.
- Plan regular monthly contributions toward a savings goal.
- Compare annual, monthly and daily compounding.
Formula
Lump sum FV = P × (1 + r ÷ m)^(m × t)P = principal, r = annual rate, m = compounding periods per year, t = years.
Equivalent monthly growth g = (1 + r ÷ m)^(m ÷ 12)Any compounding frequency is converted to a monthly factor and simulated month by month.
Each month: balance = previous balance × g + contributionContributions are added at the end of each month.
Worked example
Given: $10,000 initial, $1,000 per month, 5% a year, compounded monthly, 10 years
- g = 1 + 5% ÷ 12 ≈ 1.004167, over 120 months.
- Total contributions = 10,000 + 1,000 × 120 = $130,000.
- After 120 monthly steps the balance is about $171,752.37.
Result: About $41,752 is interest earned.
Reading the result
- Growth accelerates over time. The year-by-year table shows the later years adding the most.
- More frequent compounding helps only slightly at typical rates.
- Use a rate net of fees, or the projection will be too high.
Limitations
- A fixed-rate projection, not a forecast. Real investment returns vary and can be negative.
- Ignores inflation and taxes. Subtract expected inflation from the rate to see real purchasing power.
How to use
- 1Enter the starting amount and monthly contribution.
- 2Enter the annual rate, years and compounding frequency.
- 3Review the final balance and yearly breakdown.
FAQ
What is the compound interest formula?
A = P(1 + r/n)^(nt), where r is the annual rate, n the compounding periods per year and t the years.
Is the return guaranteed?
No. This assumes a constant rate; real investment returns vary and can be negative.
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