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CP521· Informational

CP521 — Installment agreement payment reminder

Reminder that an installment-agreement payment is due.
irs.gov primary2026-05-09
Category
Informational
Urgency
Date on notice
Response window
see notice
Key form
—

Respond by the date printed on your individual notice.

Why the IRS sent this

Active installment agreement with an upcoming scheduled payment.

Response window

Notice received
Respond bydate on your notice

The IRS detail page for CP521 does not state a fixed day count. The response-by date is printed on your individual notice — read the date at the top-right corner.

For statutory windows referenced by the IRS detail page, see the cited Publication for procedural timing.

What to do

Required action

Pay the amount shown by the due date and include the bottom portion of the notice with your payment.

Appeal path

Informal — call the IRS

Informal — call the IRS at the number on the notice.

Notes from the primary source

CP521 is a payment reminder for an installment agreement that already exists; the detail page references Form 2848 (POA) and Publication 1, but does NOT cite Form 9465 (which is for new IA requests, not existing-IA reminders).

Go deeper

Educational pillars for this notice

Calm-corrective

Only the IRS can resolve your notice

We are not a CPA firm, not a law firm, not an Enrolled Agent firm, and not affiliated with the IRS. We don't accept payments on your behalf, settle your debt, or call the IRS for you. What we do: explain what your notice means, point you to the right IRS form, cite the statute that authorizes the action, and surface the appeal path. Then you call the number on the notice, file the form, or hire a licensed professional.

Related notices

Likely next or sibling codes

Source

Verified against the official IRS detail page on irs.gov/individuals/understanding-your-cp521-notice. Always re-verify against the IRS page before acting.