Compound Interest Calculator
See how your money grows over time with the magic of compounding. Adjust your starting amount, monthly contributions, rate, and time horizon.
Inputs
How to use this calculator
1. Set your starting point
Enter your initial deposit and any planned monthly contribution. The two work together — even a modest monthly contribution can outpace a larger lump sum over decades.
2. Pick a realistic rate and horizon
Use a conservative long-term return (5-7% for diversified stock-and-bond portfolios after inflation, lower for savings accounts and CDs). The longer the horizon, the more compounding dominates.
3. Choose a compounding frequency
Annually, semi-annually, quarterly, monthly, or daily. The jump from annual to monthly is meaningful; from monthly to daily is tiny.
Why time matters more than amount
Doubling your contribution roughly doubles your final balance. Doubling your time horizon can quadruple it or more, because each new year compounds on everything that came before.
About compound interest
What is compound interest?
Interest earned on both your original deposit and the interest already accrued. Over long horizons, this snowball effect can dwarf the original principal.
Formula
For a one-time deposit: A = P(1 + r/n)nt. With monthly contributions added at period end: FV = PMT × ((1+i)k−1)/i, where i is the periodic rate and k is the number of periods.
How often does compounding really matter?
The jump from annual to monthly compounding is meaningful; from monthly to daily it's tiny. Time horizon and contribution discipline matter far more than frequency.