How Long to Double Money at 8%
At 8% a year, money doubles in 9.0 years. The Rule of 72 says 9.0.
Doubles in
9.0 years
Quadruples in
18.0 years
Grows 8 times in
27.0 years
Rule of 72 estimate
9.0 years
What different amounts become
| Start | After 9.0 years | After 18.0 years | After 27.0 years |
|---|---|---|---|
| $1,000 | $2,000 | $4,000 | $8,000 |
| $5,000 | $10,000 | $20,000 | $40,000 |
| $10,000 | $20,000 | $40,000 | $80,000 |
| $25,000 | $50,000 | $100,000 | $200,000 |
| $50,000 | $100,000 | $200,000 | $400,000 |
| $100,000 | $200,000 | $400,000 | $800,000 |
Growth over time at 8%
| Years | $1,000 becomes | $10,000 becomes | Growth |
|---|---|---|---|
| 5 | $1,469 | $14,693 | 1.47x |
| 10 | $2,159 | $21,589 | 2.16x |
| 15 | $3,172 | $31,722 | 3.17x |
| 20 | $4,661 | $46,610 | 4.66x |
| 25 | $6,848 | $68,485 | 6.85x |
| 30 | $10,063 | $100,627 | 10.06x |
| 40 | $21,725 | $217,245 | 21.72x |
| 50 | $46,902 | $469,016 | 46.90x |
How it is worked out
Years to double = ln(2) / ln(1 + r)
ln = natural logarithm, r = rate as a decimal.
The Rule of 72 is the shortcut version. Divide 72 by the rate.
At 8% the shortcut is off by 0.0 years.