If you file joint most likely his debts will confiscate your return. If you file separately it should not.

The IRS doesn't send you a notice before they keep the refund, but will send you a short note with a phone number you can call, afterwards.

The Injured Spouse form (8379) allows the IRS to calculate how much of the refund is attributable to your husband's income. Then they keep that and apply it to his debts. They do not explain exactly how they make this division. It is not subject to negotiation. If you try to claim too much on the 8379, they can ignore your information. (An example of this would be a wife who earned $2000 trying to claim all three children, when her husband made $30,000. This would be an unreasonable split of the refund.)

An 8379 is a bit of a roll-of-the-dice. It is generally better than using the Married Filing Separate filing status, since that one loses your child-related credits.

"What portion of that $3500 will I get back? He hasn't received his w-2 yet so this is only with mine."

Your joint refund number on your income alone won't be near what your refund will be once your husband's 8 months of earnings are added in. Just forget you ever saw that number, unless your husband had quite a bit of withholding done when he was working.

The Earned Income Credit, if it is showing on your joint return with only your income, may be less or gone altogether once you combine your incomes. It works on a sliding scale, then scales down until you simply make too much to qualify.

As reader stated, the formula the IRS uses with the injured spouse is not disclosed, but it's generally fair, and in your case will most likely have your household, overall, pay less tax.