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Compound Interest Calculator
The most counterintuitive thing about compounding is that its power lives almost entirely in the second half. Drag the numbers yourself and see clearly which year the money truly starts to "roll."
About the data: this calculator is a pure math tool. The annual rate is set by you and does not represent any asset's real or expected return. Crypto has no "fixed annual rate," and actual volatility can be far larger. This tool is for understanding the structure of compounding, not for predicting returns.
Why is compounding's power "all in the second half"?
Try changing the horizon from 10 years to 30, and you'll notice something counterintuitive: principal grows linearly (a fixed amount each month), but the total's growth gets steeper and steeper. The reason: later gains are earned on top of "principal + all prior gains" — the snowball rolls bigger and bigger.
This also explains why, for an ordinary person, when you start and how long you persist often matter more than "putting in a bit more each month" or "a point or two higher annual rate." Starting five years earlier beats doubling your monthly contribution.
The right way to use it
- Set the annual rate conservatively (say 6%–10%) and feel that "even without a moonshot, the long run is considerable."
- Set the annual rate negative to see what "if there's a loss" looks like — a reminder that compounding cuts both ways.
- Compare "10 years" and "20 years" to feel the free leverage of time.
To understand this thoroughly from first principles, read The compounding effect: why time beats timing.
Compounding's first step is to start
Even the most elegant compounding curve only kicks off with a "first contribution." If you've thought it through and want to DCA long-term with spare money, the next step is an account that can buy automatically.
Learn how to open an account →Disclosure: by registering through this site's links, Manfu may receive a referral service fee, and you pay nothing extra. Investing carries risk; content is for education only and is not investment advice.