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Your refund could be offset.

The IRS and State Governments have the ability to offset a refund to pay for certain past due debts.  You generally will receive a letter stating what the offset was for.   

The IRS provides a toll-free number, (800) 304-3107, to call for information about tax offsets.

Where are you seeing that half of your refund is being held?    If the IRS is saying that, only the IRS can explain.  TurboTax gets no information from the IRS after you file your tax return.