How Long to Double Money at 4%
At 4% a year, money doubles in 17.7 years. The Rule of 72 says 18.0.
Doubles in
17.7 years
Quadruples in
35.3 years
Grows 8 times in
53.0 years
Rule of 72 estimate
18.0 years
What different amounts become
| Start | After 17.7 years | After 35.3 years | After 53.0 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 4%
| Years | $1,000 becomes | $10,000 becomes | Growth |
|---|---|---|---|
| 5 | $1,217 | $12,167 | 1.22x |
| 10 | $1,480 | $14,802 | 1.48x |
| 15 | $1,801 | $18,009 | 1.80x |
| 20 | $2,191 | $21,911 | 2.19x |
| 25 | $2,666 | $26,658 | 2.67x |
| 30 | $3,243 | $32,434 | 3.24x |
| 40 | $4,801 | $48,010 | 4.80x |
| 50 | $7,107 | $71,067 | 7.11x |
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 4% the shortcut is off by 0.3 years.