Compound Interest Calculator
See how a lump sum and regular contributions grow over time.
Every calculation runs locally in your browser. Nothing you enter here is sent to a server or stored anywhere.
Final balance
$144,573
Total contributions
$58,000
Total interest earned
$86,573
Balance growth over time
For informational and educational purposes only — not financial, investment, or tax advice, and not a substitute for consulting a qualified professional about your specific situation. TrueMeasureKit is not liable for decisions made based on these results. See our Terms of Service.
How compound interest works
Compound interest is interest calculated on your initial principal and on the interest that has already accumulated. Because each period's interest is added back to the balance, growth accelerates over time — the gap between your total contributions and your final balance in the chart above is entirely interest earned on interest. The more frequently interest compounds, and the longer your money stays invested, the larger that gap becomes.
A monthly balance of $144,572.72 after 20 years reflects $58,000 in contributions plus $86,573 in compounded growth at an assumed 7% annual rate — real returns vary, so use this as a planning estimate rather than a guarantee.
Frequently asked questions
Why does compounding frequency matter?
More frequent compounding means interest starts earning its own interest sooner. The gap between annual and daily compounding is small at low rates and short horizons, but widens noticeably over decades.
What's the difference between compound and simple interest?
Simple interest is always calculated on the original principal only. Compound interest is recalculated on the growing balance each period, which is why long-term growth curves upward instead of staying a straight line.
Does this account for taxes or inflation?
No — it shows nominal growth before taxes on gains and before inflation erodes purchasing power. Use the Inflation Calculator alongside it to see what a final balance is worth in today's dollars.