CompoundHarbor
Free financial calculator

Compound Interest Calculator Pro

Calculate how your money can grow over time, or start with a target and work backwards to the savings, time, capital or return you would need.

CompoundHarbor
Capital.
Savings.
Time.
Advanced enough for serious planning, simple enough to explore in seconds.
Final portfolio
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How much will I have?
Total contributed
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Starting amount + recurring contribution
Compound growth
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Real value
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Purchasing power in today's money
Expected annual return—
Net annual return—
Real annual return—

Portfolio growth

Nominal portfolio value, contributions and inflation-adjusted value.

PortfolioContributedReal value

Year-by-year projection

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YearContributedCompound growthPortfolioReal value

Where your final value comes from

%
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Starting capital—
New contributions—
Compound growth—
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How to use this compound interest calculator

Compound interest means earning returns not only on the money you originally invested, but also on returns already accumulated. The longer the time horizon, the larger this compounding effect can become.

Compound interest formula

A = P(1 + r/n)nt

For a single lump sum, compound interest is commonly expressed as A = P(1 + r/n)^(nt), where P is the starting principal, r is the annual rate, n is the compounding frequency and t is time in years. Recurring contributions make the calculation more useful for real-world saving and investing.

Monthly contributions, fees and inflation

This calculator goes beyond the basic formula by allowing recurring contributions, contribution timing, fees, inflation, annual contribution growth, extra yearly deposits and an optional effective tax rate. You can also work backwards from a target portfolio.

Compound interest calculator FAQ

What is the difference between annual return and compounding frequency?

Annual return is the rate assumption for a full year. Compounding frequency controls how often that return is credited. The calculator converts the annual return into an equivalent rate for the selected frequency.

Why show a real value?

A future dollar may buy less than a dollar today. Real value discounts the projected portfolio by the inflation rate so you can compare future purchasing power in today's money.

Can I calculate how much I need to save each month?

Yes. Switch to “I want to reach…” and choose Required contribution. The calculator solves for the recurring amount needed under your other assumptions.

Is this investment advice?

No. This is an educational mathematical simulation. Market returns are uncertain and real outcomes can be higher or lower.