TurboTax allows you to choose to have TurboTax calculate an estimated penalty and include that amount in your balance due or you can elect to not include that in your balance due and have the IRS just bill for the penalty.
On a joint tax return paying taxes is a joint responsibility, so there is joint responsibility for any underpayment. There is no separate accounting for tax liability. Tax withholding by either spouse is credited against the joint tax liability.
