The Mega Roth is when you maximize the after-tax contribution to your 401(k) at work then convert the funds to a Roth. You then roll over or convert this amount to a Roth IRA or Roth 401k. Unlike with a normal Roth IRA conversion, the principal will not be taxable. However, the earnings portion of the rollover will be considered pre-tax and subject to taxation at the time of conversion.