Compound Interest Calculator
See how your money grows over time with compound interest and regular contributions.
Added every month
Adjusts the result to today's money
of each month
Final Balance
$144,573
After 20 years
≈ $88,229 in today's money (at 2.5% inflation)
Total Contributed
$58,000
$10,000 initial + $48,000 monthly
Interest Earned
$86,573
149% of contributions
Contributions vs. Interest Breakdown
Rule of 72: doubles every ~10.3 yrs
Investment Growth Over 20 Years
🟡 Dashed line = 2× your money milestone (year 16)
📊 Year-by-Year Breakdown▾
| Year | Balance | Contributions | Interest |
|---|---|---|---|
| 1 | $13,201 | $12,400 | $801 |
| 2 | $16,634 | $14,800 | $1,834 |
| 3 | $20,315 | $17,200 | $3,115 |
| 4 | $24,262 | $19,600 | $4,662 |
| 5 | $28,495 | $22,000 | $6,495 |
| 6 | $33,033 | $24,400 | $8,633 |
| 7 | $37,900 | $26,800 | $11,100 |
| 8 | $43,118 | $29,200 | $13,918 |
| 9 | $48,714 | $31,600 | $17,114 |
| 10 | $54,714 | $34,000 | $20,714 |
| 11 | $61,147 | $36,400 | $24,747 |
| 12 | $68,046 | $38,800 | $29,246 |
| 13 | $75,444 | $41,200 | $34,244 |
| 14 | $83,376 | $43,600 | $39,776 |
| 15 | $91,882 | $46,000 | $45,882 |
| 16 | $101,003 | $48,400 | $52,603 |
| 17 | $110,783 | $50,800 | $59,983 |
| 18 | $121,270 | $53,200 | $68,070 |
| 19 | $132,515 | $55,600 | $76,915 |
| 20 | $144,573 | $58,000 | $86,573 |
How to use this calculator
- Enter your initial principal — the amount you start with.
- Add a regular contribution if you plan to invest more over time, and set how often.
- Enter the annual interest rate and the number of years.
- Choose the compounding frequency and, optionally, an inflation rate to see the result in today’s money.
The final balance, total contributions and interest earned update as you type, with a chart of the growth curve.
How it works
Compound interest follows the formula:
A = P × (1 + r/n)^(n·t)
where P is the principal, r the annual rate, n the number of times interest compounds per year, and t the number of years. Regular contributions are added on top, each compounding from the point it is invested.
The defining feature is that interest is added to the balance and then earns interest itself. This makes growth exponential rather than linear — the curve starts gently and steepens. The two biggest levers are the interest rate and, above all, time: the longest stretches of the curve produce the most growth.
Because a large future number can be misleading, the calculator can also show the inflation-adjusted value — what the balance is genuinely worth in today’s purchasing power.
Frequently Asked Questions
What is compound interest? ▾
Compound interest is interest that earns interest. Each period, interest is calculated on the principal plus all the interest already accumulated, not just the original amount. Because the base keeps growing, the balance accelerates over time — slowly at first, then much faster. Albert Einstein is often quoted calling it the most powerful force in finance; the math is why.
How does compounding frequency affect growth? ▾
The more often interest compounds — daily, monthly, quarterly, annually — the more you earn, because interest starts earning its own interest sooner. The effect is real but modest: at typical rates, daily versus annual compounding changes the result by a small percentage. The interest rate and the time horizon matter far more.
Why does time matter so much with compound interest? ▾
Compound growth is exponential, so the later years contribute disproportionately. Money invested for 30 years does not grow twice as much as money invested for 15 — it grows far more. This is why starting early, even with smaller amounts, usually beats starting later with larger ones.
What is the difference between nominal and real (inflation-adjusted) value? ▾
The nominal final balance is the raw number. The real value adjusts that figure for inflation, showing what it is worth in today's purchasing power. A balance that looks large in 30 years buys less than the same number today — the inflation-adjusted figure tells the honest story.
How is this different from the Savings Calculator? ▾
The Savings Calculator is the simple everyday tool — steady monthly deposits, a fixed rate. This calculator adds depth: selectable compounding frequency, inflation-adjusted results, and goal-seek modes that work backwards from a target. Use this one when you need more than a straight projection.