Compound Interest Calculator
Compute future value, total interest, real returns, and year-by-year growth with contributions, inflation adjustment, and tax impact.
Regular contributions
Inflation adjusted
Tax impact
Growth chart
Year-by-year table
Free to use
Principal & Rate
$
Starting investment amount
%
Nominal annual rateCompounding & Contributions
How often interest compounds
$
Amount added each period
How often you contribute
%
Annual increase to contributionAdjustments (Optional)
%
Average annual inflation
%
Tax rate on interest earned
Display currency
Primary Results
Future Value
—
Nominal
Press Calculate
Total Contributions
—
Principal + Added
—
Total Interest Earned
—
Compound Growth
—
Real Value (Inflation)
—
Today’s Dollars
—
Growth Chart
Future Value
Total Contributions
Interest Earned
Real Value (Inflation-adj.)
Portfolio Split
Principal
—
of total future value
Contributions
—
of total future value
Interest Earned
—
of total future value
Detailed Metrics
Effective Annual Rate
—
%
EAR accounting for compounding
After-Tax Future Value
—
Net of annual tax on interest
Doubling Time
—
years
Exact calculation
Total Return
—
%
On total money invested
CAGR
—
%
Compound annual growth rate
Real Return Rate
—
%
After inflation (Fisher eq.)
Year-by-Year Breakdown
| Year | Opening Balance | Contributions | Interest Earned | Closing Balance | Real Value | Total Return % |
|---|---|---|---|---|---|---|
| Press Calculate to generate breakdown | ||||||
Formula Reference
A = P(1 + r/n)^(nt)Future value, no contributions
FV = PMT x [(1+r/n)^(nt)-1]/(r/n)Future value of annuity
EAR = (1 + r/n)^n – 1Effective annual rate
t = ln(2) / ln(1 + EAR)Exact doubling time
Real Rate = (1+r)/(1+i) – 1Fisher equation (inflation adj.)
CAGR = (FV/PV)^(1/t) – 1Compound annual growth rate
Common Questions
What is compound interest and how does it differ from simple interest?
Simple interest is calculated only on the principal: I = P x r x t. Compound interest is calculated on both the principal and accumulated interest from previous periods, creating exponential growth. For example, $10,000 at 7% for 20 years grows to $14,000 with simple interest but $38,697 compounded annually.
How does compounding frequency affect returns?
The more frequently interest compounds, the higher your effective annual rate (EAR). At 7% nominal: annually gives EAR = 7.00%; monthly gives 7.229%; daily gives 7.250%. Most savings accounts and mortgages compound monthly.
What is the Rule of 72?
The Rule of 72 is a mental shortcut: divide 72 by your annual interest rate to estimate how many years it takes to double your money. At 6%, roughly 12 years; at 9%, about 8 years. This calculator uses the exact formula: t = ln(2) / ln(1 + EAR).
How does inflation affect compound interest returns?
The real return rate uses the Fisher equation: Real Rate = (1 + nominal) / (1 + inflation) – 1. At 7% nominal and 2.5% inflation, the real return is about 4.39%. This calculator shows the real future value so you can see what your money is worth in today’s purchasing power.
Why do regular contributions matter so much?
Regular contributions dramatically accelerate wealth accumulation. Adding just $200/month to a $10,000 investment at 7% over 20 years grows the result from ~$38,700 (no contributions) to over $150,000 – more than 4x the outcome. Starting early and contributing consistently is the most powerful wealth-building strategy.
Results are for illustrative purposes only. Actual returns vary. Consult a qualified financial advisor before making investment decisions.
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