The bigger the contributions, the faster the road to $1 million

Building a $1 million 401(k) balance takes time and consistent contributions. Assuming a 7 percent return - the average rate for moderate-risk accounts - someone putting $100 a month in a 401(k) can become a millionaire in 58 years. Bumping monthly contributions up to $400 can make a saver a millionaire in 39 months.