Compound Interest Future Value Calculator
Project future value with a starting amount, monthly cash flows, compounding frequency, assumed tax on positive interest and inflation. See a year-by-year schedule.
Growth by year
| Year | Remaining balance | Cumulative net deposits / withdrawals | Cumulative net interest after assumed tax | Cumulative assumed tax | Value in today’s money |
|---|---|---|---|---|---|
| 0 | 10,000.00 | 0.00 | 0.00 | 0.00 | 10,000.00 |
| 1 | 10,511.62 | 0.00 | 511.62 | 0.00 | 10,511.62 |
| 2 | 11,049.41 | 0.00 | 1,049.41 | 0.00 | 11,049.41 |
| 3 | 11,614.72 | 0.00 | 1,614.72 | 0.00 | 11,614.72 |
| 4 | 12,208.95 | 0.00 | 2,208.95 | 0.00 | 12,208.95 |
| 5 | 12,833.59 | 0.00 | 2,833.59 | 0.00 | 12,833.59 |
| 6 | 13,490.18 | 0.00 | 3,490.18 | 0.00 | 13,490.18 |
| 7 | 14,180.36 | 0.00 | 4,180.36 | 0.00 | 14,180.36 |
| 8 | 14,905.85 | 0.00 | 4,905.85 | 0.00 | 14,905.85 |
| 9 | 15,668.47 | 0.00 | 5,668.47 | 0.00 | 15,668.47 |
| 10 | 16,470.09 | 0.00 | 6,470.09 | 0.00 | 16,470.09 |
The model applies an equivalent monthly growth rate, charges the entered tax percentage on positive monthly interest, then adds or withdraws the monthly cash flow at month end. Purchasing power discounts by the entered constant annual inflation rate. Actual tax treatment and returns vary.
About this calculation
Project how a starting amount could grow when interest is periodically added to the balance. Enter the nominal annual rate, years, and compounding periods per year. You may also add a signed monthly cash flow: positive for an end-of-month deposit and negative for a withdrawal. An assumed tax rate on positive monthly interest and an inflation rate provide additional scenario views.
Formula
Monthly growth rate = (1+r/n)^(n/12)−1; end-month contribution is then added; positive growth may be reduced by assumed tax.
Worked example
With Starting amount: 10000 currency units, Annual interest rate: 5 %, Years: 10 years, Compounds per year: 12, Monthly deposit (+) or withdrawal (−): 0 currency units, Assumed tax on positive monthly interest: 0 %, Assumed annual inflation: 0 %, future value is 16,470.09 currency units.
How periodic compounding works
If P is the starting amount, r the annual rate as a decimal, n the number of times interest is added each year, and t the number of years, the future value is FV = P(1 + r/n)^(nt). Each period adds interest to the current balance, so later periods can earn interest on earlier interest.
With 10,000 at 5% for 10 years compounded monthly, with no added cash flow or tax, the model gives about 16,470.09, including about 6,470.09 in interest. Annual compounding at the same nominal rate and term gives about 16,288.95. To model monthly cash flows consistently at any chosen compounding frequency, the calculator converts the nominal rate to an equivalent monthly growth rate of (1 + r/n)^(n/12) − 1, then applies each month’s cash flow after growth.
What annual rate are you entering?
The field expects a nominal annual rate that is divided by the selected number of compounding periods. If you have an effective annual yield or return instead, entering it here as a nominal rate can overstate growth when n exceeds one. Check how the product or scenario states its rate and compounding convention.
Monthly deposits, withdrawals and simplified tax
A positive monthly amount is deposited at each month’s end, so a new deposit starts earning growth only in later months. A negative value withdraws money at month end; the calculator warns if a scheduled withdrawal would exceed the available balance. The entered tax percentage is deducted from positive growth every month. This deliberately simple rule is not a country-specific tax calculation: real tax can depend on account type, realization, allowances, residence, and reporting period. The second result is growth after this assumed tax, calculated as ending balance minus starting amount and net monthly cash flows.
Inflation and what the scenario cannot predict
The main future value is nominal. The schedule also divides the projected balance by (1 + inflation rate)^elapsed years to show an estimate in today’s purchasing power. A zero inflation input makes that view equal the nominal value. This model does not include product fees, variable rates, market losses, tax timing rules, or irregular deposits and withdrawals. A market investment return is uncertain; a deposit product may specify another calculation convention. Compare several plausible rates and terms instead of treating one projection as a promise.
Common questions
Does more frequent compounding always add interest?
For a positive nominal annual rate and the same starting amount and time, more frequent compounding produces a higher modeled balance. The difference can be small, and real product terms still control.
Is the future value adjusted for inflation?
The primary future value is nominal. A separate schedule column shows estimated purchasing power after the inflation assumption you enter.
Can I include monthly contributions?
Yes. Enter a positive monthly contribution or a negative monthly withdrawal. The flow occurs after that month’s growth and simplified tax calculation.
Sources and references
Inputs
- Starting amount (currency units)
- Annual interest rate (%)
- Years (years)
- Compounds per year
- Monthly deposit (+) or withdrawal (−) (currency units)
- Assumed tax on positive monthly interest (%)
- Assumed annual inflation (%)