Simulate long-term wealth growth, periodic contributions, compounding frequencies, and inflation-adjusted returns.
Where A is future balance, P is initial principal, r is annual nominal interest rate, n is compounding frequency per year, t is time in years, and PMT is monthly regular deposit.
Trigger: Structuring 401(k), IRA, or taxable brokerage recurring monthly deposits.
Simulate realistic 10, 20, and 30-year accumulation curves factoring in regular salary increments and conservative real rates of return.
Trigger: Establishing a 529 education savings plan or custodial portfolio.
Determine the monthly contribution needed from birth to age 18 to fully fund anticipated higher education tuition costs.
Trigger: Evaluating compounding mechanics between daily, monthly, and annual bank deposit APYs.
Calculate the exact dollar difference between simple interest payouts and daily compounded interest accounts over multi-year terms.
Trigger: Deciding whether to spend discretionary capital on luxury depreciation.
Input the lump-sum purchase price into this engine to visualize the $100,000+ compounding opportunity cost lost over a 25-year retirement horizon.
Compounding is exponential, not linear. In the first 10 years, contributions constitute the majority of portfolio value. After 20 to 30 years, compound interest generates over 70% to 85% of total wealth creation.
Context: Investor A invests $500/month from age 22 to 32 (10 years total = $60,000 contributed) and then stops contributing completely, letting it compound until age 65. Investor B waits until age 32 and invests $500/month continuously until age 65 (33 years total = $198,000 contributed). Both earn an 8% annualized return.
Analysis & Result: At age 65, Investor A has accumulated approximately $985,000. Investor B has accumulated approximately $915,000. Investor A ends with $70,000 MORE despite contributing $138,000 LESS out of pocket.
Key Takeaway: Time in the market is mathematically more powerful than total capital contributed. Early compounding generates momentum that late contributions struggle to match.
$25,000 starting portfolio, $1,000/mo deposits for 20 years at 9% index fund return.
Result: $812,450 portfolio value
The Rule of 72 is a quick mental math shortcut: divide 72 by your annual interest rate to find the approximate number of years it takes to double your money. (e.g., 72 / 8% = 9 years to double).
Annual Percentage Rate (APR) reflects the simple annual interest rate without taking compounding into account. Annual Percentage Yield (APY) reflects the true effective annual rate of return, factoring in the effect of compounding over the course of the year. For any compounding frequency greater than once per year (e.g., daily or monthly), APY will always be higher than APR.
While daily compounding produces a slightly higher yield than monthly compounding, the difference on a $10,000 deposit at 5% over 20 years is relatively modest (approximately $27,185 with daily compounding vs. $27,126 with monthly compounding—a difference of under $60). Compounding frequency matters most at very high balances or across multi-decade corporate treasury horizons.
Yes, this is known as negative or reverse compounding. Credit card issuers compound interest on unpaid revolving balances on a daily basis. At typical credit card interest rates of 22% to 28%, balances double in approximately 2.5 to 3.2 years if only minimum payments are made, trapping consumers in a predatory compounding debt spiral.
Published Standards: Standard discrete periodic compounding formula A = P(1 + r/n)^(nt) and standard continuous compounding formula A = Pe^(rt).
Methodology: Computes discrete and continuous compounding using standard time-value-of-money (TVM) algebraic equations. Regular contributions are calculated at periodic compounding intervals with end-of-period interest accrual.
Last Updated: September 2026