Compound Interest & Investment Growth Calculator
Calculate portfolio growth with initial lump sums and recurring deposits. Supports both Beginning-of-Period (Annuity Due) and End-of-Period (Ordinary Annuity) contributions, multiple compounding frequencies, APY comparisons, and transparent mathematical formulas.
Investment Projection
Awaiting inputEnter starting principal or recurring contribution and investment horizon to calculate compound growth
Results, statistical ratios, and detailed amortization ledgers will appear here once values are provided.
Calculation Methodology & Formula
Calculates the future value of an initial investment and recurring periodic deposits using discrete compound interest mathematics. Supports both Beginning-of-Period deposits (Annuity Due) and End-of-Period deposits (Ordinary Annuity). Variable Definitions: P = initial principal, r = stated nominal annual return rate (decimal), n = compounding frequency per year (12 = monthly, 365 = daily standard 365-day convention, 4 = quarterly, 2 = semi-annually, 1 = annually), t = investment horizon in years, PMT = recurring periodic contribution, p = contribution frequency per year (12 = monthly, 1 = yearly), r_p = equivalent rate per contribution period ((1 + r/n)^(n/p) - 1), k = deposit timing indicator (k = 1 for Annuity Due, k = 0 for Ordinary Annuity), APY = ((1 + r/n)^n - 1) * 100.
FV = P(1 + r/n)^(nt) + PMT × [ ((1 + r_p)^(pt) - 1) / r_p ] × (1 + r_p)^kWorked Example: 10-Year Index Fund Accumulation (Monthly Deposits, Annuity Due)
$10,000 initial investment earning 7.0% nominal annual return with $200 deposited at the beginning of each month over 10 years.
Initial principal grows to $20,096.61. Recurring deposits total $24,000 and grow to $34,818.89. Total invested capital equals $34,000 ($10,000 initial principal + $24,000 recurring monthly deposits). Total compound interest earned is $20,915.51, representing an effective growth rate of 61.52% and an APY of 7.23%. If deposits are made at the end of each month (Ordinary Annuity), the future portfolio value is $54,713.58 with $20,713.58 in compound interest.
Technical Constraints & Limitations
- A constant annual return assumption is a deterministic mathematical projection, not a forecast or promise of market performance. Real asset returns fluctuate with market cycles and sequence-of-returns volatility.
- Excludes capital gains taxes, dividend withholding taxes, and fund expense ratios.
- Does not automatically adjust for inflation fluctuations (nominal figures displayed; use our Inflation Calculator to model real purchasing power).