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Compound Interest Calculator

Watch your money grow — contributions plus compounding returns.

Your numbers

Future value
$343,778.24
Total contributions
$130,000.00
Interest earned
$213,778.24

Breakdown

Balance growth over time

How this calculator works

Compound interest is interest earning interest — and it is the single most powerful force in long-term investing. Each period, your balance grows by the return rate, and the next period's growth is calculated on that larger balance. Add regular contributions and the effect becomes dramatic: over 20–30 years, investment growth can dwarf everything you actually put in. This compound interest calculator models exactly that, letting you set an initial amount, a monthly contribution, an assumed annual return and the compounding frequency.

Play with the two levers that matter most: time and contributions. Starting ten years earlier usually beats earning a higher return, because compounding needs time to do its heavy lifting — the growth curve stays flat for years, then bends sharply upward. Monthly contributions matter even more than most people expect; they are the fuel the compounding engine burns. The frequency setting (monthly vs daily) changes results only slightly — banks love advertising daily compounding, but the return rate and your savings habit decide 99% of the outcome. Treat the rate as a long-term average, not a promise: markets fluctuate, and this calculator shows the smooth mathematical path, not the bumpy real one.

Frequently asked questions

What is compound interest in simple terms?
You earn returns not just on your original money but on all previously earned returns too. Over time, growth accelerates because each year's gains become part of next year's base.
Does compounding frequency matter much?
Barely. The difference between monthly and daily compounding is tiny compared to the difference made by your return rate, contribution amount and time invested.
What return rate should I assume?
For long-term US stock market investing, 7–10% nominal (before inflation) is the historical range. Use 6–7% for a conservative plan and remember to subtract inflation for real purchasing power.
Is it better to invest a lump sum or monthly?
Both work. A lump sum invested earlier gets more compounding time; monthly contributions build the habit and smooth out market timing. Our calculator shows either path.
Disclaimer: Results are estimates for planning purposes only and are not financial advice. Actual loan terms, taxes and investment returns vary — consult a qualified professional before making financial decisions.