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Finance • Compound Interest Calculator

Compound Interest Calculator

Calculate future wealth accumulation with compounding frequency, monthly deposits, and total interest accrued.

Investment & Compound Growth Parameters

Future Investment Value
$113,669.42

In 10 years at 8% annual return with compounding.

Total Principal Invested
$70,000
Total Compound Interest
+$43,669
Growth Multiplier
1.62x
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Calculation Guide & Reference

Compound Interest & Future Value of a Growing Investment

Compound interest calculator projects future investment value from principal, monthly contributions, interest rate, and compounding frequency, showing total interest earned.

Standardized Mathematical Formula
FV = P(1 + r)^n + PMT × [((1 + r)^n − 1) / r]

Combines the future value of a lump-sum principal compounding over time with the future value of a series of regular contributions (an annuity), using the periodic interest rate and number of compounding periods.

Variables:
P:Initial principal (starting investment)
r:Periodic interest rate (annual rate ÷ compounding frequency)
n:Total number of compounding periods (years × frequency)
PMT:Regular contribution per period
How It Works (Step-by-Step)
  • 1Enter your initial principal (starting amount) and any regular monthly contribution.
  • 2Enter your expected annual interest rate and the number of years you plan to invest.
  • 3Choose a compounding frequency (monthly, quarterly, or annually).
  • 4View the projected future value, total amount deposited, and total interest earned.
Real-World Numerical Example
Growing $10,000 with $500 Monthly Contributions at 8% for 10 Years

An investor starts with $10,000, adds $500 monthly, earning 8% annual interest compounded monthly for 10 years.

•Monthly rate r = 8% / 12 = 0.667%.
•Periods n = 10 × 12 = 120 months.
•FV of principal: $10,000 × (1.00667)^120 = $22,196.40.
•FV of contributions: $500 × [((1.00667)^120 − 1) / 0.00667] = $91,473.20.
Result: Total future value: approximately $113,670, with $70,000 deposited and about $43,670 earned in interest.
Calculation Best Practices & Tips
Distinguish between Nominal Interest Rate (APR) and Effective Annual Yield (APY) when comparing loans or investments.
Small additional monthly principal payments on mortgages can dramatically shorten amortization schedules and save tens of thousands in cumulative interest.
Factor in inflation when forecasting long-term investment purchasing power over 10-30 year time horizons.

Frequently Asked Questions (FAQ)

Simple interest is calculated only on the original principal each period; compound interest is calculated on the principal plus all previously earned interest, so growth accelerates over time rather than staying linear.

It has a modest effect — monthly compounding versus annual compounding at the same nominal rate typically adds a small amount more over long periods, though the effect is smaller than most people assume compared to the rate itself and contribution amount.

Significantly — because compound growth is exponential, money invested a decade earlier has far more compounding periods to grow, often outperforming a much larger sum invested later, all else being equal.

No, this shows nominal (pre-tax, pre-inflation) growth based on your inputs. Real purchasing power growth will be lower after accounting for taxes on gains and inflation eroding value over time.

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