How to determine the amount each spouse should pay when filing a joint return?

[DoninGA]

On a joint tax return there is no way to determine the taxes owed from each spouse.

You can look at your paperwork, W-2's and Form 1099's, to find out the total income for each spouse and use the percentage contributed for each spouse.

[rjs]

You can split the payment due in any way that seems fair to the two of you. On a joint return nothing is calculated separately for each person. The tax and the payment due are calculated on your total combined income, the amount of tax that the two of you together have to pay on that combined income, and the total combined amount of tax that you paid through withholding or estimated tax payments. There are no individual amounts.

[Mike9241]

since the spouse may have different types of income subject to different tax rates another way (often available in software used by professionals) is to calculate taxes as if MFS. then the joint tax is apportioned in relation to the MFS tax (before reduction for withholding and estimated tax payments). Then from the apportion amount each taxpayer's withholding and estimated tax payments are subtracted. Issues do arise if the taxpayers itemize or if there are tax credits. the parties would have to agree on how they are to be allocated.