Compound Interest Calculator
Compound interest pays you interest on your interest, so a balance grows faster the longer it is left alone. Enter a starting balance, a rate, a time horizon, and any monthly contribution to see the final balance and how much of it is pure growth.
- Accurate
- Real-time
- Easy to use
- 100% free
Final balance
$144,572.72
Total interest
$86,573
Details
Updates as you typeThe nominal yearly rate, before compounding is applied.
Added at the end of every month, on top of the starting balance.
Summary
Compounding is doing the work — 75%+Final balance
$144,572.72
Final balance
$144,572.72
- Starting balance$10,0007%
- Contributions$48,00033%
- Interest earned$86,57360%
- Total contributed
- $58,000
- Total interest
- $86,573
- Growth on what you put in
- 149.3%
- Effective annual rate
- 7.229%
- Time horizon
- 20 years
- Contributions are assumed to arrive at the end of each month and to earn the same rate from then on.
- The rate is assumed constant. Real returns vary, and taxes and inflation are ignored.
How this is calculated
- Starting balance
- $10,000
- Nominal annual rate
- 7.000%
- Compounding periods per year
- 12
- Rate per period
- 0.5833%
- Starting balance grown alone
- $40,387
- Monthly contributions grown
- $104,185
- Final balance
- $144,573
- Contributed over the period
- $48,000
- Interest earned
- $86,573
Years
Compare scenarios
See how one change moves the result
- CurrentYour inputs as they stand$144,572.72Current
- Starting balance$ 12,500$154,669.57
- Annual interest rate% 8.75$186,594.75
- Years to growyr 25$219,268.52
For informational purposes only. This is not financial advice — confirm major decisions with a licensed advisor.
Frequently asked questions
What is compound interest?
Compound interest is interest calculated on your original balance plus all the interest already earned. Because each period starts from a larger balance, growth accelerates over time instead of staying flat like simple interest.
Does compounding frequency really matter?
Less than most people expect. At 7% a year, monthly compounding beats annual compounding by roughly 0.23 percentage points of effective yield, and daily adds only a sliver more. The rate itself and the number of years matter far more.
How are monthly contributions handled here?
They are treated as an ordinary annuity: each contribution arrives at the end of its month and then earns the same rate for the months remaining. The future value of that stream is added to the growth of your starting balance.
What is the rule of 72?
Divide 72 by your annual percentage rate to estimate the years needed to double your money. At 8% that is about nine years. It is an approximation, but a very quick sanity check on any long-run projection.