By requesting innocent spouse relief, you can be relieved of your responsibility for paying tax, interest, and penalties if your spouse (or former spouse) improperly reported items or omitted items on your tax return. Generally, the tax, interest, and penalties that qualify for relief can only be collected from your spouse (or former spouse). However, you are jointly and individually responsible for any tax, interest and penalties that do not qualify for relief. The IRS can collect these amounts from either you or your spouse (or former spouse). Innocent spouse relief only applies to individual income or self-employment taxes. The IRS will figure the tax for which you are responsible.
The IRS will consider all of the facts and circumstances of the case in order to determine whether it is unfair to hold you responsible for the understatement.