Sure, doubling your money in 10 seconds would be way more exciting… Just head to Vegas and stick it all on red!
But when it comes to building real, long-term wealth, my goal is to simply double my net worth every 10 years.
All it takes is earning a 7.2% average return each year. That’s it. And thanks to low-cost index funds and no-fee accounts, it’s actually super achievable — even if you know nothing about investing.
The Rule of 72 and doubling your money
Here’s the rule of thumb that changed how I thought about long-term wealth.
The Rule of 72 says: Divide 72 by your average annual return, and you’ll get the number of years it takes to double your money.
So, if your investments grow 1% per year, it would take 72 years to double your money (72 divided by 1).
At 4%, it’ll take about 18 years. And at a 7.2% annual return, it doubles in 10 years.
The cool realization for me was this… When you leave your money for multiple decades, it can double over and over again.
Here’s a look at what $10,000 turns into when earning an average 7.2% return over multiple decades:
|
Time |
Future Value |
|---|---|
|
10 years |
$20,042 |
|
20 years |
$40,169 |
|
30 years |
$80,508 |
|
40 years |
$161,358 |
Data source: Author’s calculations.
Understanding how compound interest worked made me naturally save more. My thinking was that for every $1,000 I save today, it has the potential to become $8,000 in 30 years.
Why I love index funds
So, how do I earn a 7.2% annual return?
I’ve been investing for a while now, and I’ve tried a few different strategies.
I’ve gone too risky chasing massive gains (and failed miserably). And I’ve played it too safe sometimes, barely earning anything at all.
Eventually, I settled into an “index and chill” strategy. Index funds are perfect for me because they’re completely passive, widely diversified, and my portfolio achieves average market returns.
Most of my retirement money is in a broad-market index fund, similar to the S&P 500, which has averaged about 10% annually over its long history.
Of course, past performance doesn’t guarantee future returns. But even a slightly lower return still clears the 7.2% target I’m aiming for to double my money every decade.
I use Fidelity accounts mostly. But any low cost broker that doesn’t nickel-and-dime you with monthly fees or high expense ratios is a good choice.
Consistent investing and keeping track
If you’re just getting started — or feel behind on retirement savings — the best thing you can do is set up an automatic savings system.
Part of my “set it and forget it” strategy is investing every single month, no matter what. I use my workplace 401(k) plan (and you should too if you have access to one — especially if you’ve got an employer match). I also invest in a Roth IRA and after-tax brokerage accounts.
No matter which type of account you use, the key is to turn on automatic investing so you don’t have to think about it each month. Set up paycheck deductions, or automatic transfers each month.
And here’s the second part of the system: I track my net worth every couple of months. If you’re new to this, it’s just a running tally of your assets (like your cash, investments, home equity) minus your liabilities (like credit cards, student loans, or a mortgage).
Net worth = What you own – What you owe
That number doesn’t need to be perfect, but it gives me a high-level view of whether my investments and savings are moving in the right direction.
The bottom line
Doubling your net worth in 10 years isn’t some magical feat — it’s just math. I’ve done it (and then some) by using simple index funds and automatic investing.
If you’re just getting started, don’t overthink it. Invest a little each month, track your progress, and let time do the rest.
And if you’re looking for help starting out, check out our best investment apps for beginners in 2025. Remember, $1,000 invested today can grow to $8,000 later with average market returns.
