Total Contributions
$58,000.00
Compound Interest Calculator
Project growth of a lump sum (plus optional regular contributions) over time.
Future Value
$144,572.72
Interest Earned
$86,572.72
From Lump Sum
$40,387.39
From Contributions
$104,185.33
What is the Compound Interest Calculator?
Compound interest is interest earning interest. This calculator projects how a starting balance — plus any regular contributions — grows when returns are reinvested period after period. It's the engine behind savings accounts, retirement funds and long-term investing, and the reason starting early matters more than starting big.
The formula
Future value combines a growing lump sum with a growing stream of contributions:
FV = P(1 + r)ⁿ + C · ((1 + r)ⁿ − 1) ÷ r- P
- initial principal
- C
- contribution added each period
- r
- periodic rate = annual rate ÷ compounding periods per year
- n
- total periods = years × periods per year
The first term grows what you start with; the second grows everything you add along the way.
Worked example
Start with $10,000, add $200 every month, and earn 7% a year compounded monthly for 20 years.
The balance grows to $144,572.72. You contributed $58,000 of that — the other $86,572.72 is compound interest, more than the money you put in.
Prefer your own numbers? Enter them in the calculator above — it recomputes instantly.
Key terms
- Compounding frequency
- How often interest is added back to the balance — annually, monthly, daily.
- Principal
- The initial amount you invest before any growth.
- Contribution
- Money you add on a regular schedule, which itself starts compounding.
- Future value
- What the balance is projected to be worth at the end of the term.
Frequently asked questions
Does compounding frequency matter?
More frequent compounding earns slightly more, but the effect is small next to the rate and the time horizon.
Why does time matter so much?
Growth is exponential, so the earliest dollars do the most work. Ten years of a head start usually beats a larger contribution later.
Is the result guaranteed?
No. A fixed rate is an assumption; real investment returns vary year to year. Treat the figure as a projection, not a promise.