Compound Interest Calculator
See how a lump sum and regular monthly contributions grow over time with compounding.
Added at the start of each month.
Final balance
$343,778.24
Total contributed
$130K
Interest earned
$213.78K
Frequently asked questions
What is compound interest?
Compound interest is interest calculated on the initial principal plus all the accumulated interest from previous periods. The more frequently interest compounds, the faster your balance grows.
How often should interest compound?
More frequent compounding (daily vs. annually) increases your returns, though the difference is small at low rates. A 7% annual rate compounded daily yields roughly 7.25% effective annual return.
What rate should I assume for long-term investing?
The S&P 500 has returned roughly 7% annualized after inflation over the past century. High-yield savings accounts currently pay 4–5%. Picking a conservative rate (6–7%) keeps projections realistic.