How Long Does It Take Money to Double?
At 7% it takes about 10 years. At 2% it takes 35.
The table below has every rate from 1% to 15%.
The Rule of 72 column is the mental shortcut. The exact column is the real answer.
| Rate | Exact years | Rule of 72 | Quadruples in |
|---|---|---|---|
| 1% | 69.7 | 72.0 | 139.3 years |
| 2% | 35.0 | 36.0 | 70.0 years |
| 3% | 23.4 | 24.0 | 46.9 years |
| 4% | 17.7 | 18.0 | 35.3 years |
| 5% | 14.2 | 14.4 | 28.4 years |
| 6% | 11.9 | 12.0 | 23.8 years |
| 7% | 10.2 | 10.3 | 20.5 years |
| 8% | 9.0 | 9.0 | 18.0 years |
| 9% | 8.0 | 8.0 | 16.1 years |
| 10% | 7.3 | 7.2 | 14.5 years |
| 11% | 6.6 | 6.5 | 13.3 years |
| 12% | 6.1 | 6.0 | 12.2 years |
| 13% | 5.7 | 5.5 | 11.3 years |
| 14% | 5.3 | 5.1 | 10.6 years |
| 15% | 5.0 | 4.8 | 9.9 years |
Why doubling time matters
Doubling time turns an abstract rate into something you can picture. A 7% return means your money doubles roughly every decade.
Over a 40 year working life that is four doublings. $10,000 becomes $160,000 without adding a cent.
It works for inflation too. At 3% inflation prices double every 23 years, so a dollar buys half as much.