On a joint tax return there's really no way to determine how much of the tax each spouse is responsible for. You don't "each owe separately." Everything on a joint return is pooled. Your total tax is calculated on your total taxable income. Your deductions are added together and the totals are subject to a single set of thresholds and limits. A change in one person's income or deductions can affect the other person's income or deductions. You don't each pay a certain amount of tax. The two of you together pay the total tax.
