I’m having trouble paying my taxes. What interest does the IRS charge on the outstanding amount?

The IRS interest rate on underpayments is set quarterly. For the third quarter of 2020 (July 1 through September 30), the rate for an individual is 3%. Interest compounds daily. It’s wise to request an installment payment agreement to get outstanding taxes under control. Interest will continue to accrue on the balance, but eventually, the debt will be gone.