I live in Missouri and need to know if i need to file an injured spouse since my wife had no income but owes child support?

[RBBrittain]

Generally, your best option is to file a joint return with the injured spouse form. Though the IRS will take longer to process Form 8379, it still allows you to get your best refund on a joint return without losing your own money to an IRS tax offset for your wife's child support. This is especially true if your wife has no income, as that maximizes the tax benefit of filing jointly while minimizing her tax payments & credits that could be used for child support.

[yadi441]

is there a way to tell how much would go to her offset if not filing an injured spouse

[RBBrittain]

If you don't file an injured spouse form, they'll take the entire refund up to whatever she owes.