My husband and I owe this year, less than 10K. What is the current interest on a payment plan to the IRS?

Under the Internal Revenue Code, the rate of interest is determined on a quarterly basis and is currently 6% for individual taxpayers.

For individual taxpayers, the overpayment and underpayment rate is the federal short-term rate plus 3 percentage points.

Does this change if we are still paying after April 15th (i.e. late fees)?

If you file your return by its due date and request an installment agreement, the late penalty fee is 0.25% for any month in which an installment agreement is in effect.