If an IRA rollover is not completed properly, the IRS may consider the rollover as a withdrawal rather than a transfer.
In general, the best way to roll over your 401(k) account to an IRA is to do it without any tax consequences or penalties. If an IRA rollover is not completed properly, the IRS may consider the rollover as a distribution/withdrawal rather than a transfer. If the funds are distributed or withdrawn it may be subject to income taxes and early withdrawal penalties (if the distribution occurs before you are age 59.5).
Here’s what you need to do to accomplish a tax-free, penalty-free rollover. The first thing to do it make sure that your former employer’s 401(k) plan allows you to roll over the assets in your account to an IRA. You can do this by contacting your former employer’s Human Resources department or the administrator of your former employer’s 401(k) plan. Most 401(k) plans allow it but if your former employer’s plan does not, find out what options are available to you. If the plan does allow it, you have two general ways to do it – as a direct rollover or as an indirect rollover.
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http://www.boston.com/business/personalfinance/managingyourmoney/archives/2011/11/the_best_way_to.html