Section 401(a)(31) of the tax code requires that they allow a direct rollover on any eligible rollover distribution, so if they allow in-service distributions, they are also required to allow a direct rollover of the otherwise taxable portion of such a distribution. Since they are only required to allow a direct rollover of the taxable portion of a distribution, if you are doing a split rollover of pre-tax and after-tax amounts, a plan will often do the direct rollover to a traditional IRA of the pre-tax amount, avoiding mandatory 20% tax withholding, and will pay the after-tax amount to you (with no tax withholding because this portion is nontaxable) which you can then roll over indirectly within 60 days to a Roth IRA.
You always get credit for the withholding no matter what. You have 60 days to roll it into a Traditional IRA to avoid the tax. But you need to add back in the withholding from your own money or the withholding will become a taxable distribution by itself.
Section 401(a)(31) of the tax code requires that they allow a direct rollover on any eligible rollover distribution, so if they allow in-service distributions, they are also required to allow a direct rollover of the otherwise taxable portion of such a distribution. Since they are only required to allow a direct rollover of the taxable portion of a distribution, if you are doing a split rollover of pre-tax and after-tax amounts, a plan will often do the direct rollover to a traditional IRA of the pre-tax amount, avoiding mandatory 20% tax withholding, and will pay the after-tax amount to you (with no tax withholding because this portion is nontaxable) which you can then roll over indirectly within 60 days to a Roth IRA.
Talk to your IRA custodian and tell them you want to roll the 401K funds to the IRA ... they should take care of everything for you.