Category
Finance
Compound Interest Calculator
See how your investments grow over time with compound interest
Estimated time
2 min
Enter Investment Details
Project long-term growth from an initial amount and recurring contributions.
$
Amount added each month. Contributions are assumed to be made at the end of each month.
$
Expected annual return rate before taxes and fees. Enter 7 for a 7% yearly return assumption.
%
How often interest is added to the balance. More frequent compounding can increase long-term growth.
Compounding Insights
- Time in market often matters more than timing the market.
- Recurring contributions can outpace one-time contributions over long periods.
- Small rate differences compound into large value differences over decades.
How Compound Growth Is Calculated
The calculator grows your initial principal and adds future value from monthly contributions.
A = P(1 + r/n)^(nt) + PMT * ((1 + r/12)^(12t) - 1) / (r/12)
A- final amount
P- initial principal
r- annual interest rate (decimal)
n- compounding periods per year
t- time in years
PMT- monthly contribution amount
- Time horizon has the biggest impact on compound growth.
- Consistent monthly contributions can drive most long-term value.
- Higher compounding frequency slightly increases value at the same rate.
- Compare final value with total contributed to measure investment growth.
Example Scenarios
Long-term IRA style saving
$10,000 initial + $200/month at 7% for 20 years
Strong compounding from consistency
Aggressive contribution plan
$5,000 initial + $500/month at 8% for 30 years
Contributions drive most growth early
Lump sum only
$25,000 initial, no monthly contribution at 6% for 15 years
Growth depends fully on market return
Frequently Asked Questions
Does compounding frequency matter a lot?
It matters, but time horizon and contribution size usually matter more.
Why are my contributions compounded monthly?
This assumes contributions are made each month and start compounding immediately.
What rate should I use?
Use conservative long-run assumptions and consider inflation for real return planning.
Does this account for taxes?
No. Taxes and fees are not included in this estimate.
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