That means that the interest rate or ROI must equal 7% on average over the next 50 years.
Not that much of a dream ... normally I = 4%.
Applying the Rule of 72
72/(I=7.2%)
Doubles 4.5 times to get from 30K to 650k in 50 years
30K
60K
120k
240k
480k
960k
Einstein is attributed with the saying "There is no force in the universe more powerful than compound interest," and that he in fact invented the famous Rule of 72.
The Rule of 72, as you may recall, tells us how many years are required for an investment to double, by dividing the interest rate into 72.
For example, an investment paying 8% will double in approximately 9 years, because 72 divided by 8 equals 9.
This simple arithmetic computation is not exact, but it is close enough to the exact results of a logarithmic equation to make it extremely useful.
As for Einstein? No proof can be found that he ever even mentioned the Rule of 72, much less invented it.
In fact, it was first cited nearly 400 years before Einstein's birth, by Italian friar Luca Pacioli, in his 1494 book “
Summa de arithmetica geometria, proporzioni et proporzionalita,” a guide to arithmetic, algebra, geometry, accounting and weights and measures.