№ 020 · Investing cluster
Compound Interest Calculator
The eighth wonder of the world, quantified. See how an initial amount and steady monthly contributions snowball over the years — and how much of the final number is pure growth.
Monthly compounding
Want today’s-dollar values and contributions that grow each year? Try the Investment Growth Calculator. Locking a lump sum at a fixed, guaranteed rate instead? See the CD Calculator. Putting it off? The Cost of Waiting Calculator shows what a late start costs.
Starting point01
$
$
Growth02
%
yr
Future value · 30 years
$691,150.47
73% from growth$190,000.00 contributed
Total contributed$190,000.00
Total interest$501,150.47
Initial amount$10,000.00
Growth multiple3.64×
- Balance$691,150.47
- Contributed$190,000.00
| Year 1 | balance $16,919.19, contributed $16,000.00 |
|---|---|
| Year 2 | balance $24,338.58, contributed $22,000.00 |
| Year 3 | balance $32,294.31, contributed $28,000.00 |
| Year 4 | balance $40,825.16, contributed $34,000.00 |
| Year 5 | balance $49,972.70, contributed $40,000.00 |
| Year 6 | balance $59,781.53, contributed $46,000.00 |
| Year 7 | balance $70,299.43, contributed $52,000.00 |
| Year 8 | balance $81,577.68, contributed $58,000.00 |
| Year 9 | balance $93,671.22, contributed $64,000.00 |
| Year 10 | balance $106,639.02, contributed $70,000.00 |
| Year 11 | balance $120,544.25, contributed $76,000.00 |
| Year 12 | balance $135,454.70, contributed $82,000.00 |
| Year 13 | balance $151,443.02, contributed $88,000.00 |
| Year 14 | balance $168,587.14, contributed $94,000.00 |
| Year 15 | balance $186,970.62, contributed $100,000.00 |
| Year 16 | balance $206,683.03, contributed $106,000.00 |
| Year 17 | balance $227,820.45, contributed $112,000.00 |
| Year 18 | balance $250,485.91, contributed $118,000.00 |
| Year 19 | balance $274,789.85, contributed $124,000.00 |
| Year 20 | balance $300,850.72, contributed $130,000.00 |
| Year 21 | balance $328,795.53, contributed $136,000.00 |
| Year 22 | balance $358,760.48, contributed $142,000.00 |
| Year 23 | balance $390,891.60, contributed $148,000.00 |
| Year 24 | balance $425,345.48, contributed $154,000.00 |
| Year 25 | balance $462,290.03, contributed $160,000.00 |
| Year 26 | balance $501,905.30, contributed $166,000.00 |
| Year 27 | balance $544,384.37, contributed $172,000.00 |
| Year 28 | balance $589,934.26, contributed $178,000.00 |
| Year 29 | balance $638,776.94, contributed $184,000.00 |
| Year 30 | balance $691,150.47, contributed $190,000.00 |
Year by year
| Year | Contributed | Interest | Balance |
|---|---|---|---|
| 1 | $16,000.00 | $919.19 | $16,919.19 |
| 2 | $22,000.00 | $2,338.57 | $24,338.58 |
| 3 | $28,000.00 | $4,294.30 | $32,294.31 |
| 4 | $34,000.00 | $6,825.15 | $40,825.16 |
| 5 | $40,000.00 | $9,972.70 | $49,972.70 |
| 6 | $46,000.00 | $13,781.52 | $59,781.53 |
| 7 | $52,000.00 | $18,299.42 | $70,299.43 |
| 8 | $58,000.00 | $23,577.66 | $81,577.68 |
| 9 | $64,000.00 | $29,671.21 | $93,671.22 |
| 10 | $70,000.00 | $36,639.00 | $106,639.02 |
| 11 | $76,000.00 | $44,544.24 | $120,544.25 |
| 12 | $82,000.00 | $53,454.69 | $135,454.70 |
| 13 | $88,000.00 | $63,443.01 | $151,443.02 |
| 14 | $94,000.00 | $74,587.13 | $168,587.14 |
| 15 | $100,000.00 | $86,970.60 | $186,970.62 |
| 16 | $106,000.00 | $100,683.01 | $206,683.03 |
| 17 | $112,000.00 | $115,820.44 | $227,820.45 |
| 18 | $118,000.00 | $132,485.89 | $250,485.91 |
| 19 | $124,000.00 | $150,789.83 | $274,789.85 |
| 20 | $130,000.00 | $170,850.70 | $300,850.72 |
| 21 | $136,000.00 | $192,795.52 | $328,795.53 |
| 22 | $142,000.00 | $216,760.47 | $358,760.48 |
| 23 | $148,000.00 | $242,891.59 | $390,891.60 |
| 24 | $154,000.00 | $271,345.47 | $425,345.48 |
| 25 | $160,000.00 | $302,290.02 | $462,290.03 |
| 26 | $166,000.00 | $335,905.30 | $501,905.30 |
| 27 | $172,000.00 | $372,384.37 | $544,384.37 |
| 28 | $178,000.00 | $411,934.25 | $589,934.26 |
| 29 | $184,000.00 | $454,776.94 | $638,776.94 |
| 30 | $190,000.00 | $501,150.47 | $691,150.47 |
How it works · methodology
The math, in the open.
A = P(1 + r/n)^(nt) + PMT · [ (1 + r/n)^(nt) − 1 ] / (r/n) Future value = compounded principal + compounded contributions
- P
- Initial principal
- PMT
- Contribution each period
- r
- Annual nominal rate
- n
- Compounding periods per year (12)
- t
- Years
Assumptions & limits
- Interest compounds monthly; contributions are added at the end of each month.
- The rate is nominal and constant — real markets vary year to year and this does not subtract inflation.
- Taxes and fees are not modeled.
- Results are estimates for education, not a promise of returns.
By the MintNumber Editorial Team·Reviewed
Frequently asked
Questions about compounding
What is compound interest?
Compound interest is interest earned on both your original money and the interest it has already earned. Over time the growth accelerates, because each period’s interest is added to the balance that earns the next period’s interest.
How often does interest compound?
This calculator compounds monthly, which is typical for investment accounts. More frequent compounding produces slightly higher returns than annual compounding at the same nominal rate.
What return rate should I use?
The U.S. stock market has returned roughly 7% per year after inflation (about 10% before) over the long run, but any single decade can be very different. Use a conservative figure and treat the result as an estimate, not a promise.
Is this real or nominal growth?
The rate you enter is nominal — it does not subtract inflation. To see growth in today’s dollars, use a lower real rate (for example, 7% nominal minus ~3% inflation ≈ 4% real).