FTF = 5%/mo of unpaid tax, max 25% (§6651(a)(1)); reduced to 4.5%/mo when FTP runs concurrently. FTP = 0.5%/mo of unpaid tax, max 25% (§6651(a)(2)). Interest = federal short-term rate + 3% per §6621; 7% APR for the Q4 2026 quarter (the rate changes each quarter). Partnership/S-Corp penalty = $255/partner/month for 12 months max (returns due in 2026) (Rev. Proc. 84-35 may abate small partnerships). First-Time Abatement available if clean past 3 years. 689-331-5723 · info@zerofusstaxes.com