At a steady return, money doubles on a predictable schedule. Here's yours.
A 'how long to double my savings' calculator tells you how many years an investment takes to grow to twice its value at a given rate of return, and shows both the exact figure and the quick Rule of 72 estimate.
Divide 72 by your annual return and you get a close estimate of the years to double: about 9 years at 8%, 12 years at 6%, 7.2 years at 10%. It's remarkably accurate for the mid-single-digit to low-double-digit rates most investors deal with. At very high rates the shortcut drifts from the precise logarithmic answer, which this calculator computes exactly alongside the estimate.
Because doubling time depends on the rate in a compounding, not linear, way, small differences in return compound into large differences in time. Money earning 4% takes about 18 years to double; at 8% it's about 9 years, twice as fast for double the rate. Over a long horizon that gap is the difference between doubling once and doubling two or three times, which is why fees and return assumptions deserve close attention.
Roughly 72 divided by your annual return in percent. At 8% that's about 9 years; the calculator also shows the exact figure.
A mental-math shortcut: 72 ÷ annual return ≈ years to double. It's accurate for typical investment returns and handy for quick comparisons.
Yes, it assumes returns are reinvested and compound each year. Without compounding, doubling takes much longer.
See the exact formula and a worked example on our methodology page.