Compound Interest Calculator

Compounding frequency specifies how many times each year accrued interest is capitalized into your principal balance. The more frequently interest is credited, the faster that new interest begins generating its own return.

The exact conversion between nominal annual interest rate (APR) and effective annual percentage yield (APY) is: APY = (1 + r / n)^n - 1, where r is the nominal APR and n is compounding periods per year.

For a $10,000 balance at 8.0% APR: Annual compounding yields $800.00 (8.00% APY); Monthly compounding yields $830.00 (8.30% APY); Daily compounding yields $832.78 (8.33% APY). Over 30 years, monthly compounding produces $109,357.30 compared to $100,626.57 for annual compounding—a $8,730.73 difference purely from frequency.

The Rule of 72 provides a rapid mathematical approximation for how many years it will take an investment balance to double at a fixed annual return: Doubling Years ≈ 72 / Annual Return Rate (%).

At a 6% annual return, capital doubles in approximately 12 years (72 / 6). At 8%, it doubles in approximately 9 years (72 / 8). At 10%, it doubles in approximately 7.2 years.

Over a 36-year horizon: at 6%, an initial sum doubles 3 times (8x); at 8%, it doubles 4 times (16x); at 10%, it doubles 5 times (32x). This demonstrates how small differences in average annual return create exponential divergence in final net worth.

Our calculator utilizes the standard ordinary annuity formula, assuming recurring monthly contributions are deposited at the end of each payment period.

Depositing contributions at the beginning of each period (annuity due) generates one additional compounding period of interest for each deposit. Over a 30-year timeframe, beginning-of-period deposits generate roughly 0.6–0.8% higher total ending value.

Nominal future value represents the raw dollar amount in your future account, but does not reflect future purchasing power.

To project real purchasing power in today's dollars, subtract estimated annual inflation from your nominal expected rate (e.g., 8.0% nominal return minus 2.5% inflation equals a 5.5% real return), or apply the exact Fisher equation: Real Return = (1 + Nominal Rate) / (1 + Inflation Rate) - 1.