Compound Interest & Wealth Growth Calculator

Simple interest is calculated strictly on the initial principal amount (Interest = Principal × Rate × Time). In contrast, compound interest calculates interest on both the original principal AND all previously accumulated interest. Over multi-decade investment horizons, compounding generates exponential growth where accumulated interest dwarfs total principal deposits.

The more frequently interest is compounded, the higher the effective annual yield (APY). For example, $10,000 at 8% annual return over 20 years yields $46,610 compounded annually, $49,268 compounded monthly, and $49,521 compounded daily. While more frequent compounding yields higher balances, continuous recurring contributions generally exert a far larger impact on final wealth than the frequency difference alone.

The Rule of 72 is a practical mental math shortcut to estimate how many years it takes for an investment to double at a fixed annual rate of return: Doubling Years ≈ 72 / Annual Interest Rate. At an 8% return, your money doubles in approximately 72 / 8 = 9.0 years (actual formula yields 9.006 years). It is remarkably accurate for returns between 4% and 12%.

Inflation diminishes the real purchasing power of future dollars over time. While an investment portfolio may grow nominally to $1,000,000 in 30 years at 7%, a 3% annual inflation rate reduces its real purchasing power to roughly $411,987 in today's purchasing terms using the Fisher equation: Real Value = Nominal Value / (1 + Inflation)^Years.

A seemingly small 1.0% annual management or mutual fund fee does not reduce your return by 1%—it strips away 25% to 35% of your total lifetime nest egg over a 30 to 40 year horizon. Because the 1% fee is deducted from the entire balance every single year regardless of market performance, you permanently lose both the deducted capital and the exponential compound interest that money would have generated.