Modifier –51 (Multiple Procedures) is used when the same provider performs multiple procedures in the same session to identify secondary, non‑exempt procedures and indicate payment reduction logic may apply. Per CPT/AMA guidance, the highest‑valued procedure is reported first without –51; subsequent procedures that are not E/M, physical medicine/rehab, supplies, add‑ons, or listed as modifier‑51 exempt are appended with –51. Many payers (including Medicare) have internal multiple procedure payment reduction (MPPR) logic—typically paying the primary procedure at 100% and reducing second through fifth procedures (commonly to ~50%)—so modifier –51 may be descriptive rather than required. Always confirm payer rules because some insurers ignore the modifier or apply reductions automatically; unnecessary use when only one procedure is billed can cause an inadvertent payment cut.