The Power of Compound Interest: Why You Should Start Investing at 25 Instead of 35

Einstein is said to have called compound interest "the eighth wonder of the world." Whether or not the quote is real, the numbers don't lie: time matters more than money when investing for the long term.

What is compound interest?

Compound interest is interest earned on both principal and accumulated interest. In the first year you earn interest on your principal; the following year, interest is calculated on principal plus the previous year's interest — a snowball that grows bigger as it rolls.

How much is starting 10 years earlier worth?

Compare two people both investing 3 million VND/month, assuming 8% annual return, both stopping at age 60:

An contributes only 360 million VND more in principal than Binh, but ends up with 4 billion VND more. That gap is the first 10 years of compound interest — something you can't buy back with money.

Three principles to harness compound interest

1. Consistency matters more than large amounts: 2 million/month for 20 years beats a one-time 50 million then stopping. Automate transfers on payday.
2. Don't interrupt: withdrawing midway means restarting the snowball from scratch. This is why you need an emergency fund before investing — so you won't have to sell assets during tough times.
3. Fees also "compound": a 2% annual management fee sounds small, but over 30 years can erode 30–40% of your results. Prioritize low-cost, transparent channels.

Where does the 8% return come from?

That's an illustrative assumption, close to the expected long-term return of a balanced portfolio (index fund equities + bonds + deposits). Actual returns fluctuate year by year and aren't guaranteed — the only things you can control are time in the market, consistent contributions, and costs.

Try your own scenarios with [Sirifin's compound interest calculator](/vi/calculators/compound-interest) — change the number of years to see the gap for yourself.

Content is informational and for financial education purposes, not investment advice.