QONTIFY
// DOUBLING TIME CALCULATOR

Doubling Time Calculator

Find out how long money takes to double at a chosen annual return.

// INPUTS
The compounded annual rate.
// OUTPUT
EXACT DOUBLING TIME
9.01 yrs
RULE OF 72 ESTIMATE9.00 yrs
RULE OF 70 ESTIMATE8.75 yrs

// FORMULA

// FORMULA
Years = ln(2) / ln(1 + r)
r is the annual return as a decimal. Use the Rule of 72 (72 / r%) for a quick mental estimate.

// EXAMPLE

// WORKED OUT
At 8% per year:
  Years = ln(2) / ln(1.08)
        = 0.6931 / 0.0770
        = 9.01 years
Rule of 72: 72 / 8 = 9.00 years

// WHAT THIS MEANS

Doubling time is one of the cleanest ways to feel a compounding rate. At 8% it takes about 9 years, at 12% about 6 years, and at 20% only 3.8 years. The Rule of 72 is a good mental shortcut, especially in the 6–10% range where it is most accurate.

// FAQ

How accurate is the Rule of 72?+
Within ~1% of the exact answer for rates between 5% and 12%. It overestimates slightly at very low rates and underestimates at very high rates.
Why does the exact formula use logarithms?+
Because doubling is an exponential question: you are solving for the exponent n in (1 + r)^n = 2, which rearranges to n = ln(2)/ln(1+r).
Does this account for taxes or fees?+
No — the return you enter should already be net of any costs you want to bake in.

// RELATED CALCULATORS

// COMPOUNDING
Return Required to Double
What annual return is needed to double in N years.
// COMPOUNDING
Rule of 72 Calculator
Quick doubling-time approximation.
// RETURN MATH
CAGR Calculator
Annualized growth rate between two values.
// COMPOUNDING
Investment Growth Calculator
Future value of a lumpsum at a chosen rate.