Average 401k return last 20 years. With regard to a 401(k), experts estimate annual rate of returns to be around 5% to 8%. To estimate how long (on average) it’ll take to double your money, divide your estimated rate of return into 72. Therefore, if your current rate of return is 6%, it’ll take about 12 years to double your money. Keep in mind that while a return of 5% to 8% is common, it’s not guaranteed. Some years your account may see a much higher rate of return, and other years Write down the current value of your 401 (k) investments and the original value of the 401 (k) at the beginning of the year. Deduct the original value of your 401 (k) from its current value. Divide the result by the original value and multiply by 100. This is your 401 (k)'s rate of return. Your 401 (k) plan 's rate of return is directly correlated to the investment portfolio you create with your contributions, as well as the current market environment. That being said, although each 401 (k) plan is different, contributions accumulated within your plan,