Back to All IRS Notices
Medium PriorityPayment Plan

CP521

Installment Agreement Reminder

Complete guide for tax professionals on responding to IRS CP521 notices, including deadlines, required documentation, and response strategies.

Response Deadline

By due date shown

IRS: 1-800-829-1040View on IRS.gov

What Triggers This IRS Notice

  • 1Monthly installment agreement payment is due
  • 2Reminder of ongoing payment obligation

What the IRS Is Claiming

  • Your monthly payment is due
  • The amount and due date are specified
  • Continued compliance is required to maintain agreement

Key Deadlines and Response Timelines

Payment is due by the date shown on the notice. Missing payments can result in default and resumption of collection action.

What Happens If You Do Not Respond

  • Missed payment can default the agreement
  • Collection action may resume
  • Additional penalties and interest
  • May need to renegotiate agreement

Documentation Commonly Required

Copy of the CP521 notice
Records of payments made
Bank statements showing payment history

When IRS Information Is Incorrect

  • 1
    Provide proof of payment if already paid
  • 2
    Contact IRS to correct account issues

How Tax Professionals Typically Respond

  1. 1

    Make the payment by the due date

  2. 2

    Set up automatic payments to avoid missing due dates

  3. 3

    Contact IRS immediately if you can't make the payment

  4. 4

    Request modification if circumstances have changed

IRS Notice Copilot

Let AI analyze this notice and draft a professional response letter in minutes.

  • Tracks all installment agreement deadlines
  • Sends payment reminders before due dates
  • Monitors agreement compliance
  • Prepares modification request if needed

15 credits (~$15) per notice — no subscription

Related Notices

CP2000

Income Discrepancy Notice

CP14

Balance Due Notice

CP501

Reminder Notice

CP503

Second Reminder Notice

CP504

Intent to Levy Notice