Compound Interest Calculator
Project future value, contributions, and inflation-adjusted growth with the WealthCalcLab compound interest calculator.
Updated April 5, 2026
What this calculator does
This compound interest calculator shows how money can grow when returns are reinvested and contributions continue over time. It works for savings accounts, deposits, conservative investments, and long-range planning scenarios where compounding is the main driver of results.
Compounding matters because growth starts earning growth of its own. The longer the time horizon, the more useful it becomes to separate the portion created by your own contributions from the portion created by reinvested returns.
United States savers and investors can use the calculator to compare steady contribution plans, account for fee drag, and test the real purchasing-power value of the projected balance after inflation.
How to use it
Enter your starting amount, monthly contribution, expected annual rate, and time horizon.
Choose a compounding frequency if you want to model a deposit account or product with a specific compounding convention.
Use Advanced options to include inflation and annual fee drag before interpreting the final number.
Formula
Future value without contributions = P × (1 + r ÷ m)^(m × t)Projection with contributions is simulated monthly using an effective growth rate.P is the starting amount, r is the annual rate, m is compounding periods per year, and t is time in years.
Methodology
The calculator converts the chosen annual rate and compounding frequency into an effective monthly projection rate, then simulates growth month by month.
Monthly contributions are added before growth is applied for that month, producing a practical planning estimate rather than a purely academic closed-form result.
Inflation adjustment is shown separately so you can compare nominal future value with estimated real purchasing power in United States terms.
Worked example
An account that starts with 10,000 and receives 300 per month can grow far beyond the sum of deposits if the return is steady and the time horizon is long.
The inflation-adjusted figure is often the most honest number when planning for long-term goals because it reminds you that nominal balances do not tell the whole story.
How to interpret the results
Future value is the projected nominal ending balance. Contributions show how much capital came from you directly. Growth shows how much came from compounding.
If the inflation-adjusted value is much lower than the headline future value, your return assumptions may need to be revisited in real terms.
Common mistakes
- Assuming a quoted rate is guaranteed for the full projection horizon.
- Ignoring fees, taxes, or inflation when using long-term growth figures for planning.
- Using unrealistic contribution levels that are difficult to sustain consistently.
Key terms
Quick definitions for the finance terms that matter on this page.
Compound interest
Growth earned not only on the original amount but also on previously accumulated interest or returns.
Real value
The inflation-adjusted value of money expressed in today’s purchasing-power terms.
Frequently asked questions
Clear answers on assumptions, interpretation, and the limits of each estimate.
What if I make no monthly contributions?
The calculator still works. It will show how the initial amount grows on its own through compounding.
Why does inflation-adjusted value matter?
Because a nominal balance can look large years from now while buying less than expected in real terms.
Does this calculator include taxes automatically?
No. It includes fee drag and inflation, but tax treatment depends on the product and jurisdiction.
Is daily compounding always much better than monthly?
Usually the difference is small compared with the effect of time horizon, contribution rate, and the headline annual return.
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Important disclaimer
Calculator outputs are estimates only and should not be treated as financial, tax, legal, or investment advice.