Compound Interest Calculator
Calculate how your savings or investment grows with compound interest. Supports monthly contributions and any compounding frequency. Runs entirely in your browser.
Future value
$144,572.72
Total contributions
$58,000.00
Total interest earned
$86,572.72
Year-by-year balance
| Year | Balance | Interest so far |
|---|---|---|
| 1 | $13,201.42 | $801.42 |
| 2 | $16,634.27 | $1,834.27 |
| 3 | $20,315.28 | $3,115.28 |
| 4 | $24,262.39 | $4,662.39 |
| 5 | $28,494.83 | $6,494.83 |
| 6 | $33,033.24 | $8,633.24 |
| 7 | $37,899.74 | $11,099.74 |
| 8 | $43,118.03 | $13,918.03 |
| 9 | $48,713.55 | $17,113.55 |
| 10 | $54,713.58 | $20,713.58 |
| 11 | $61,147.34 | $24,747.34 |
| 12 | $68,046.20 | $29,246.20 |
| 13 | $75,443.79 | $34,243.79 |
| 14 | $83,376.14 | $39,776.14 |
| 15 | $91,881.93 | $45,881.93 |
| 16 | $101,002.60 | $52,602.60 |
| 17 | $110,782.60 | $59,982.60 |
| 18 | $121,269.60 | $68,069.60 |
| 19 | $132,514.70 | $76,914.70 |
| 20 | $144,572.72 | $86,572.72 |
How compound interest works
Compound interest is the engine behind long-term wealth building. Unlike simple interest — which is calculated only on the original principal — compound interest is calculated on an ever-growing base that includes previously earned interest. The result is exponential growth: the longer you stay invested, the faster the balance climbs.
The formula
The standard compound interest formula is FV = P × (1 + r/n)n×t, where
P is the starting principal, r is the annual interest rate as a
decimal, n is the number of compounding periods per year, and t is
the number of years. When you add regular monthly contributions, each deposit compounds for the
remainder of the year it is made, building on top of the formula above.
Key inputs explained
- Principal — the lump sum you invest or deposit today.
- Annual rate — the stated yearly interest or return rate.
- Years — how long you leave the money invested.
- Compounding frequency — how often interest is added (daily, monthly, quarterly, annually).
- Monthly contribution — an optional fixed amount added each month, like a recurring savings transfer or SIP.
Reading the results
The calculator shows three headline figures — future value (what you end up with), total contributions (what you actually put in), and total interest (the free money compounding gave you). The year-by-year table lets you see the growth curve and identify when the interest earned starts to overtake your new contributions — the hallmark of compounding working in your favour.
Frequently Asked Questions
What is compound interest?↓
Compound interest means you earn interest on your interest — not just on the original principal. Over time this creates an exponential growth curve rather than a straight line. For example, $1,000 at 5% compounded monthly for 10 years grows to ~$1,647, whereas simple interest only gives $1,500.
How does compounding frequency affect the result?↓
The more frequently interest compounds, the more you earn. Daily compounding produces slightly more than monthly, which produces more than annual. For most savings accounts and investments the difference is modest, but over decades even a small increase in frequency adds up meaningfully.
How are monthly contributions handled in the formula?↓
Each monthly deposit is added to your balance and then earns compound interest for the remaining portion of the year. Over 10 years of $200/month at 6%, your $24,000 in contributions grows to roughly $32,800 — the extra $8,800 is pure compound growth on those contributions.