How many doubles can you get?
Instead of asking “what’s the return?” start asking “How many doubles can I get?”
The Rule of 72 makes it easy to figure out how long it takes to double your money.
7% return will take ~ 10 years to double (72/7)
10% will take ~ 7 years (72/10)
15% will take ~ 5 years (72/15)
20% will take ~ 3.5 years (72/20)
And the number of years you leave your money untouched determines how many doubles you will get. Over a 10 year period:
7% return ~ 1 double (10 years / 10 years to double once)
10% ~ 1.5 doubles (10/7)
15% ~ 2 doubles (10/5)
20% ~ 3 doubles (10/3.5)
There Are Only 3 Things That Matter In Investing
Starting capital
Length of the runway - how long will you stay invested
Rate of return
If your runway is long enough, the first two matter less because time is what powers the doubles.
Starting At 18 vs Starting At 42
Imagine you start with 5000.
At 18, with a 50 year runway at 10% returns, the money doubles every 7 years. Over 50 years it doubles 7 times. That turns the 5000 into 500,000.
At 42, with a 25 year runway at the same 10%, you only get 3.5 doubles. That turns 5000 into 50,000.
Same return. Same capital. But the 18-year-old ends up with 10x more simply because of time. This is why compounding is called the eighth wonder of the world.
If you’re young, invest the first part of your income, not what’s left over. And if you’re in your 40s, don’t despair. You’ve got more capital now, and even a couple of doubles in 20 years can leave you with more money than you can spend.
I am going to make sure that my kids enter the game early and get in the habit to save and invest the first part of their savings and not their last. The length of their runway will ensure that they don’t have to make herculean decisions.
Should You Go For The Slow Path Or The Fast Path?
Of course, the faster your money doubles, the more wealth you create. A 20% return gets you 3 doubles in a decade instead of 1.5 at 10%. But chasing high returns is riskier if you don’t know what you are doing.
Mohnish Pabrai, the billionaire investor, pointed out that only 4% of companies in the US stock market generate 96% of the returns. The reason you buy the index is because you own that 4% as well. If you try to pick stocks, you’re betting on your ability to identify the 4%, the 1 in 25 winners, and only invest in them. You better know what you’re doing because you are competing against some very smart people and algorithms who are also after this 4%.
How Many Doubles Has Warren Buffett Got?
Warren Buffett started investing when he was 11. He has been at it for 83 years (1942 → 2025). Given the length of his runway he would have become rich even if he had just left his money in the index. But he had the skills to go after the 4%.
Let’s see his performance with the lens of doubles.
S&P 500 (10% CAGR)
Rule of 72: 72 ÷ 10 = 7.2 years per double
Total doubles: 83 years ÷ 7.2 ≈ 11.5 doubles
Growth factor: 2^11.5 ≈ 2,900
Initial investment needed to reach $1M today:
1,000,000 ÷ 2,900 ≈ $345
In the S&P, he would have needed about $350 in 1942 to reach $1M today.
Warren Buffett (20% CAGR)
Rule of 72: 72 ÷ 20 = 3.6 years per double
Total doubles: 83 ÷ 3.6 ≈ 23 doubles
Growth factor: 2^23 ≈ 8.4 million
Initial investment needed to reach $1M today:
1,000,000 ÷ 8,388,608 ≈ $0.12
Buffett only needed about 12 cents in 1942 to reach $1M today.
The difference between 11.5 doubles of the index and 23 doubles with Buffett choosing to pick his own stocks is $350 initial investment vs 12 cents initial investment to become a millionaire today. I think it is fair to say that he knew how to identify the 4%.
What I Chose To Do
I am no Warren Buffett. But I want to be like Dick Holland, the man who identified Buffett’s talent and gave him his money to manage. In return Warren Buffett made him go through more doubles than the index would have.
I chose to go after the 4% through Marcellus. I discovered them in 2020, read their books, followed their content and interacted with them before I took an informed decision to let them manage my investments. Over the next two decades, I believe that I will get more doubles with Marcellus than if I bought the index. The worse case scenario I believe is that they will match the index returns.
Useful Idea
No matter what you do, think in terms of doubles.
Don’t just ask “What’s my return?”
Ask “How many times will my money double?”
Because that’s how small sums quietly grow into fortunes.
👋 I’m Harsh. I build businesses with people I like and share useful ideas for making better decisions — to live a Happy & Rich life.
Here’s where I spend most of my time:
iDeals Virtual Data Rooms – helping IB, PE & Corp Dev close deals faster
M&A Community – where dealmakers connect, learn and grow
Happy Ratio – loaded wraps that make healthy eating delicious
Marcellus Investment Managers – compounding wealth the right way
Zero1 by Zerodha – a curated network of high quality storytellers that build what this generation needs and not what it needs to be sold.
Harsh Batra (Connect with me on LinkedIn)