My spouse and I keep separate finances. is there a way to figure our separate tax obligations, even though we filed jointly?

[600deluxe]

He is over 65. I am not.

[600deluxe]

I already paid in full. I want to know what to charge him.

[MinhT]

When you file jointly, you have a joint tax obligation to the IRS.

It is not very easy to separate your respective tax obligations as income, withholding, deductions and credits are claimed together on a joint return.

[600deluxe]

Can I create additional "single" returns (not to be filed) to get the split ratio?

[MinhT]

If you create 2 separate mock single returns, the tax due will be different as the single tax rates are different from the Filing jointly tax rate. What you could perhaps do is to allocate your respective tax burdens by the income of each of you.