Utility tool
Compound Interest Calculator
Estimate the future value of a lump sum plus monthly contributions with compound interest.
Free｜No sign-up｜Files stay on your device
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Support us／Ko-fiAbout Compound Interest Calculator
Compounding rewards time. Enter your starting amount, monthly contribution, expected return and years to see your future balance — and how much of it is growth.
It assumes monthly compounding at a constant rate. Real returns vary, so treat it as a planning estimate.
Great for
- ・Index fund contribution plans
- ・Retirement goals
- ・College savings
How to use
- 01Fill in each field.
- 02Results are calculated instantly below.
Why use it
Private by design
Everything runs locally in your browser. Nothing passes through a server.
Instant
No software to download and no account to create.
Works everywhere
Desktop, phone, or tablet — any modern browser.
Free forever
No watermarks and no usage limits.
Frequently asked questions
What is the Rule of 72?
+
Divide 72 by your annual return to estimate how many years it takes to double your money. At 6% a year, that's about 12 years.
How accurate is this?
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It assumes monthly compounding at a constant rate. Real returns fluctuate and fees and taxes aren't included — this is an estimate, not financial advice.
Is this tool free? Do I need an account?
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It's completely free. There's no sign-up, no login and no usage limit.
Are my files and data safe?
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Everything is processed inside your browser. Your files are never uploaded to our servers and disappear when you close the page.
Does it work on my phone?
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Yes. The page is fully responsive and works in current versions of Chrome, Safari and Edge on iPhone, Android and tablets.
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compound interest calculator/investment calculator/savings calculator/future value calculator