Compound Interest Calculator
Understand how time, monthly investing, expected returns, and inflation shape long-term wealth.
What this calculator shows
It separates the money you contribute from the growth created by compounding, then discounts the result for inflation so the outcome is easier to compare in today's purchasing power.
Inputs
Adjust the assumptions and watch the outcome update instantly.
- Final nominal value
- $660,849
- Inflation-adjusted value
- $315,055
- Total contributions
- $190,000
- Investment gains
- $470,849
Before inflation.
Purchasing power today.
Money invested.
Growth earned.
- Nominal value
- Inflation-adjusted
- Contributions
Nominal value shows the account balance. Inflation-adjusted value estimates what that balance may feel like in today's purchasing power.
Year-by-year breakdown
A table makes the chart inspectable and shows how contributions, gains, and inflation-adjusted value change each year.
| Year | Nominal value | Inflation-adjusted | Contributions | Gains |
|---|---|---|---|---|
| 1 | $16,890 | $16,478 | $16,000 | $890 |
| 2 | $24,263 | $23,093 | $22,000 | $2,263 |
| 3 | $32,151 | $29,856 | $28,000 | $4,151 |
| 4 | $40,592 | $36,774 | $34,000 | $6,592 |
| 5 | $49,623 | $43,860 | $40,000 | $9,623 |
| 6 | $59,287 | $51,123 | $46,000 | $13,287 |
| 7 | $69,627 | $58,575 | $52,000 | $17,627 |
| 8 | $80,692 | $66,227 | $58,000 | $22,692 |
| 9 | $92,530 | $74,091 | $64,000 | $28,530 |
| 10 | $105,197 | $82,180 | $70,000 | $35,197 |
| 11 | $118,751 | $90,506 | $76,000 | $42,751 |
| 12 | $133,254 | $99,082 | $82,000 | $51,254 |
| 13 | $148,772 | $107,922 | $88,000 | $60,772 |
| 14 | $165,376 | $117,041 | $94,000 | $71,376 |
| 15 | $183,143 | $126,454 | $100,000 | $83,143 |
| 16 | $202,153 | $136,175 | $106,000 | $96,153 |
| 17 | $222,494 | $146,222 | $112,000 | $110,494 |
| 18 | $244,258 | $156,610 | $118,000 | $126,258 |
| 19 | $267,547 | $167,358 | $124,000 | $143,547 |
| 20 | $292,465 | $178,483 | $130,000 | $162,465 |
| 21 | $319,128 | $190,004 | $136,000 | $183,128 |
| 22 | $347,657 | $201,942 | $142,000 | $205,657 |
| 23 | $378,183 | $214,315 | $148,000 | $230,183 |
| 24 | $410,846 | $227,147 | $154,000 | $256,846 |
| 25 | $445,795 | $240,458 | $160,000 | $285,795 |
| 26 | $483,191 | $254,272 | $166,000 | $317,191 |
| 27 | $523,205 | $268,613 | $172,000 | $351,205 |
| 28 | $566,019 | $283,506 | $178,000 | $388,019 |
| 29 | $611,831 | $298,978 | $184,000 | $427,831 |
| 30 | $660,849 | $315,055 | $190,000 | $470,849 |
Your contributions are 28.8% of the final value — the other 71.2% was created by compounding, not by saving harder.
Contributions vs growth
Your contributions represent 28.8% of the final nominal value. 71.2% of the final nominal value came from investment growth.
Inflation changes the story
Inflation reduces purchasing power by $345,794, or 52.3% of the nominal ending value.
Starting earlier matters
Starting 5 years earlier adds $301,624, bringing the ending value to $962,473. That is a 45.6% difference under the same assumptions.
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Try the Savings Goal CalculatorHow the calculation works
This is an educational model, not a forecast. It uses a steady annual return assumption, compounds monthly, adds contributions at the end of each month, and discounts future value by the inflation rate.
Compounding
Each month, the current balance grows by the monthly equivalent of the expected annual return. The next month starts from that larger or smaller balance.
Inflation adjustment
Future dollars are discounted back to today's purchasing power so the nominal result does not hide the cost of inflation.
Related concepts
Keep exploring the ideas behind long-term compounding.
Frequently asked questions
Common questions about compound interest, how it's calculated, and inflation.
What is compound interest?
Compound interest is the interest you earn on both your original money and on the interest it has already earned. Over time this creates a snowball effect, so growth accelerates the longer you stay invested.
How is compound interest calculated?
The core formula is future value = principal × (1 + rate)^time, with contributions added along the way. This calculator compounds monthly and adds your regular contributions, then shows the year-by-year balance so you can see how it builds.
What is the difference between simple and compound interest?
Simple interest is calculated only on your original amount, so it grows in a straight line. Compound interest is calculated on your original amount plus accumulated interest, so it grows faster and faster over time.
How much will my investment grow?
It depends on your starting amount, contributions, expected return, and time horizon — all of which you enter as assumptions. Small changes to the return or the number of years can make a large difference, which the chart and yearly table make visible. These are estimates, not forecasts.
Does this calculator account for inflation?
Yes. Alongside the nominal balance, it shows the inflation-adjusted value in today's dollars, so you can see what your future balance would actually be worth. The inflation rate is an assumption you choose.
How often does interest compound here?
This model compounds monthly using a geometric monthly rate derived from your annual return. Monthly compounding is a common, reasonable assumption for long-term investing; real-world results vary.
This is one of several educational models on Rionux. See how we model these projections across all our tools.
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Educational use only
Educational purposes only. Calculator results are estimates based on assumptions and user inputs. They are not financial, investment, legal, or tax advice. Investing involves risk, including possible loss of principal. Past performance does not guarantee future results.