Where did the 401(k) start? It’s a tax code! The code was implemented with the Revenue Act of 1978. The shift from pensions (defined benefit plans) to 401(k) (defined contribution plans) began during this time period in history. People once relied on the company to provide income during retirement and now the responsibility is on the YOU! Today there are limited quantities of pension plans available at companies and they are most commonly provided through federal and state governments.