Last time, we looked at how compounding turns a steady monthly saving habit into a much larger sum over time. This time, the question is simpler: how long does it actually take for your own money to double? Catch up on the power of compounding interest here.
There’s a quick way to work that out, without a calculator. It’s called the Rule of 72.
The Rule of 72
It works like this. Take the number 72. Divide it by your annual return. The answer is roughly how many years it takes your money to double.
72 ÷ return rate = years to double.
That’s the whole formula. No spreadsheet needed.
What This Looks Like in Practice
| Annual Return | Rule of 72 Estimate | Real Example |
|---|---|---|
| 5% | 14.4 years | A savings account |
| 10% | 7.2 years | A fixed deposit or bond fund |
| 15% | 4.8 years | A balanced portfolio |
| 20% | 3.6 years | A strong equities year |
The Rule of 72 is a quick estimate, not an exact figure. It gets you close enough to plan with.
Why This Matters
Notice how much the return rate changes the wait. At 5%, doubling your money takes about 14 years. At 15%, it takes under 5 years, less than a third of the time.
The rate you earn doesn’t just add up over time. It compounds. A small difference in return, kept up for years, becomes a very large difference in outcome.
This is also why compounding accelerates the way it does. Each doubling happens faster when the rate of growth is higher, and every doubling builds on the one before it.
What This Means for You
- Know your rate. Before you invest, ask what average annual return to expect. That number decides how long you’ll wait to double your money.
- Small rate differences matter. Moving from 10% to 15% doesn’t just add a little extra. It can cut your doubling time by almost a third.
- Use it to set expectations. The Rule of 72 is a fast way to sense-check any investment claim someone makes to you.
This article is for general investor education and is not financial or investment advice. Speak to a licensed adviser before making investment decisions.