Compound Interest Calculator with Contributions, Fees & Inflation
Estimate how an initial investment may grow with compound interest. Model monthly or annual deposits and withdrawals, changing contributions, investment fees, inflation, and annual, monthly or daily compounding. Compare the nominal future value with its estimated purchasing power after fees and inflation.
Compound Interest
How to use this compound interest calculator
Enter a starting amount, annual interest or return rate, compounding frequency and investment period. You can then add regular deposits, withdrawals, or both. Optional fee and inflation assumptions let you compare the nominal balance with an estimate of real purchasing power.
Regular cash flows are applied at the end of their scheduled period. Monthly deposits therefore begin compounding after they are added, rather than being treated as though they had been invested from the start of the year.
What the results mean
Nominal final value
The nominal final value is the projected balance before the separate fee and inflation adjustments shown by the real-value series. It reflects the return, compounding convention, deposits and withdrawals entered in the calculator.
Real final value after fees and inflation
The real final value applies the entered annual fee assumption to the adjusted balance and then discounts that balance for cumulative inflation. This provides an estimate of future purchasing power in today's money rather than simply showing a future nominal amount.
Net capital committed
Net capital committed is the initial investment plus deposits actually made, less withdrawals actually taken from the nominal balance. It helps separate cash contributed from the effect of compounding.
Effective annual rate (APY)
The APY shows the effective annual rate implied by the entered nominal annual rate and selected compounding frequency. For example, monthly or daily compounding can produce an effective annual rate above the stated nominal rate.
Calculation methodology and assumptions
The calculator advances the projection month by month so recurring cash flows and partial years are time-weighted. Annual compounding is represented by the equivalent monthly growth rate (1 + r)^(1/12) - 1; monthly compounding uses r / 12; daily compounding is converted to its equivalent monthly rate from (1 + r/365)^(365/12) - 1. Deposits and withdrawals are applied after that month's growth.
Annual fees are converted to an exact effective monthly deduction using 1 - (1 - fee)^(1/12). Inflation is applied separately when calculating real purchasing power. The model assumes constant rates and smooth compounding. It does not model taxes, market volatility, sequence-of-returns risk, transaction costs, currency movements or product-specific rules.
Compound interest with monthly contributions
Recurring contributions can have a large effect over long periods because each contribution receives its own remaining time to compound. This calculator time-weights monthly contributions rather than giving later deposits a full year's return. You can also increase the contribution each year by either a percentage or a fixed amount.
Compound interest with withdrawals
Use the withdrawal option to explore how regular cash outflows interact with compound growth. Withdrawals may be monthly or annual and can increase over time. The calculator limits an actual withdrawal to the available nominal balance so it does not count cash that could not have been withdrawn.
Fees, inflation and purchasing power
A future balance can look substantially larger in nominal terms while having less purchasing power after investment costs and inflation. Showing both values makes those effects visible instead of hiding them inside a single return assumption.
Frequently asked questions
What is compound interest?
Compound interest is growth earned not only on the original capital but also on growth accumulated in earlier periods. The effect becomes more significant as the time horizon increases.
Can I calculate compound interest with monthly contributions?
Yes. Select deposits, enter the amount and choose monthly frequency. You can also specify an annual percentage or fixed increase in the contribution.
Can I include investment fees and inflation?
Yes. The calculator accepts separate annual assumptions for fees and inflation and displays a real final value after both effects.
Does it support annual, monthly and daily compounding?
Yes. The selected compounding convention is converted into a monthly simulation rate so monthly cash flows and partial years are handled consistently.
Is the result a forecast?
No. It is a mathematical scenario based on the assumptions entered. Actual investment returns, inflation and costs vary over time and may differ materially from the inputs.
Educational use only. This calculator does not provide investment, financial, tax or legal advice. See the InvestCalcs disclaimer for important limitations.