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The Rule of 72 Made Me Take Investing Seriously—Here’s Why

By Beelinger Staff
Estimated read time: 4 minutes

I used to think investing was something for “later.” Like, future-me-in-my-40s kind of later. I was focused on surviving rent, groceries, and those random car repairs that always seem to show up at the worst time.

But then I stumbled on a simple math formula that made me rethink everything: the Rule of 72.

What Is the Rule of 72?

The Rule of 72 is a shortcut to estimate how long it will take your money to double, based on your annual return rate.

The formula: 72 ÷ interest rate = years to double

So if you’re earning 6% on your investments: 72 ÷ 6 = 12 years to double your money.

If you’re earning 1% in a savings account? That’s 72 years. Yep—seven decades.

Why It Woke Me Up

Seeing it spelled out like that hit hard. I realized that leaving my money in a low-interest account was costing me more than I thought. Not just cents… but years of progress.

That’s when I started researching beginner-friendly investing platforms and learning how compound interest actually works.

What I Did Next

I opened an account with Fidelity and started with index funds.
I set up auto-investments of $50 every paycheck.
I stopped trying to “time the market” and focused on consistency.

📈 Quick Math: At 8% interest, your money doubles every 9 years. At 10%, it doubles every 7.2 years. Now imagine what that means over 30 years.

The Takeaway

The Rule of 72 made something click: the earlier you start, the easier it is to win.

You don’t need thousands to begin investing—you just need time and consistency. The rest will snowball on its own (thanks, compound interest).

If your money isn’t working for you, it’s losing value to time. The Rule of 72 helped me stop waiting—and start building real wealth, one small step at a time.