What is compound interest?
Compound growth means gains are calculated on both the original amount and on growth already earned. Over long periods, the curve can look dramatic on a chart. Charts are not promises.
Assumptions that change the story
- A fixed annual rate every year (markets do not work that way)
- No fees, taxes, or gaps in contributions
- No withdrawals for emergencies
Try a conservative rate and a mid case in the compound interest calculator. Compare “start earlier with less” versus “start later with more.” The goal is intuition, not a forecast you can take to a bank.
Related: monthly saving and compounding.
Disclaimer: Educational only. Not investment advice. Past or hypothetical returns do not guarantee future results.
Last reviewed: 2026-09-14.
Inflation and fees
A nominal rate that ignores fees and inflation overstates purchasing-power growth. Even modest annual costs compound against you in the same mathematical way returns compound for you. When comparing products, read expense ratios and tax treatment rather than only the headline rate field in a calculator.
Sequence of returns matters for withdrawals in retirement; a growth toy that assumes a flat rate every year cannot show that risk. Use the tool to build intuition about time and contribution size, then study real product documents.
How this guide fits the site
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