Form 15100 – ATIN Extension, Eligibility, Timing, Steps

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An adoption is still pending, the family has been filing under an Adoption Taxpayer Identification Number, and that ATIN is about to lapse. Form 15100 asks the IRS to extend it for one more year while a Social Security number still cannot be obtained.

It is a one-page request that rewards precision. There is no e-file option, both adoptive parents sign in original ink, and you fax it to (855) 250-1731 or mail it to the Austin service center at Stop 6182. Use it only to extend an existing ATIN; a brand-new ATIN goes on Form W-7A instead, and if a Social Security number has already arrived, you check the box and write it in so the IRS can retire the ATIN.

Key Takeaways

• Use Form 15100 only to extend an existing ATIN that is nearing the end of its two‑year window, do not use it to request a new ATIN.
• When the IRS sends a reminder, usually about three months before expiration, they include Form 15100 with CP notices such as CP561A or CP562C. Respond before the expiration date.
• If you need a brand‑new ATIN, file Form W‑7A and include placement documentation. ATIN applications typically take about 4 to 8 weeks, and the Austin ATIN Unit can be reached at 737‑800‑5511 (not a toll-free line, so long-distance charges may apply) if you have no update after eight weeks.
• If you already received a Social Security number for your child, check the SSN-received box on Form 15100 and write in the assigned SSN so the IRS can retire the ATIN.
• You can reply by fax or mail to the address in your notice. Read the deadlines on your CP letter, many responses are due within 60 days.

What Form 15100 Does, and When You Need It

Form 15100 exists for one job, extending an Adoption Taxpayer Identification Number that is close to expiring while the adoption is still pending. The IRS places ATINs on a two‑year clock. As your clock nears the end, you will usually receive CP561A telling you the ATIN will expire in about three months, or CP562C asking for more information to process your extension. The notice includes Form 15100 and gives you the precise steps and deadlines.

Two points matter for timing. First, do not wait for the expiration date. Second, an extension adds one more year when you cannot yet obtain an SSN. Your notice will spell out what to include, for example the reason you need the extension, why an SSN is not available yet, and the status of the case.

If the adoption is not finalized before the ATIN expires, request an extension using the instructions in your reminder notice, then keep an eye on the response deadline and method.

Quick Decision Check, Which Form Do You Actually Need?

• You have no ATIN yet and cannot get an SSN in time, file Form W‑7A to request an ATIN.
• You already have an ATIN and it will expire soon, use Form 15100 to request an extension (you must include a written reason for the delay, a checked box alone is not enough).
• You received an SSN after the adoption finalized, check the SSN-received box on Form 15100 and write the assigned SSN so the IRS can retire the ATIN and update your record.

Who This Guide Helps

• Parents finalizing a domestic adoption who need to file on time and keep benefits in order
• Accountants and enrolled agents who manage seasonal crunches and cannot afford delays or rejected dependents
• Firm administrators who want a repeatable checklist that anyone on the team can run with

In our work supporting accounting teams, we see most delays come from unclear form selection, missing signatures, and mailing to the wrong place. The fix is a simple flow and a short checklist you can reuse every season.

The What‑How‑Wow Snapshot

• What, Form 15100 extends an existing ATIN about to expire.
• How, follow your CP notice, complete the fields exactly as they appear on the account, and send it by fax or mail before the deadline.
• Wow, you can often keep your return moving without drama by pairing 15100 with a calendar reminder, a one‑page checklist, and a quick status call at the eight‑week mark if you are still waiting on an ATIN decision for a related W‑7A.

Do You Need Form 15100, Eligibility and Timing

To be eligible, you must already have a valid ATIN that is approaching its two‑year expiration, the adoption is still pending, and an SSN is not yet obtainable. The IRS will send you a reminder with Form 15100 and instructions on what to include, such as why the adoption is not final and why an SSN is not available. Answer before the deadline on the notice, many letters give a 60‑day window.

Common signs you are in the right place, you received CP561A saying the ATIN expires in three months, or CP562C asking for more details to process your extension. If you missed a deadline or the ATIN already expired, read your latest notice for next steps, then call the Austin ATIN Unit if needed.

Real‑World Example

A client’s ATIN was issued in February 2024, and CP561A arrived in November 2025 warning of a February 2026 expiration. They could not get an SSN yet because the court date moved. We completed Form 15100 the same week, included the reason for delay, and submitted it by fax as shown in the notice. The extension arrived in time, their return stayed accurate, and no credits were lost.

Alternatives and Next Steps, W‑7A, SSN, and Form 15100

You do not always need Form 15100. Sometimes the right move is to request a brand‑new ATIN with Form W‑7A, other times you should report a newly issued SSN on Form 15100 itself, by checking the SSN-received box, so the ATIN is retired. Use the quick map below to decide fast, then follow the steps that match your situation.

Comparison, W‑7A vs 15100 vs the SSN-received path

Purpose	Use this when	What you include	Outcome
Form W‑7A	You do not have an ATIN yet and cannot get an SSN because the adoption is not final	Placement papers, identification details, basic adoptive parent info	IRS assigns an ATIN so you can file and claim eligible tax benefits
Form 15100	You already have an ATIN and it is close to the two‑year expiration, the adoption is still pending	ATIN, adoptee and parent names, current address, written reason for the delay, signature	IRS extends the ATIN so you can keep filing without interruption
Form 15100 (SSN-received box)	The adoption has finalized and the child now has an SSN	The new SSN, updated address if changed, any notice number from the CP letter	IRS retires the ATIN and updates your record to the SSN

Think of it this way, W‑7A starts the ATIN, 15100 keeps the ATIN alive when the clock is running out, and the SSN-received box on 15100 ends the ATIN once you have the SSN.

When to Use W‑7A

Start with W‑7A if a child has been placed with you for a domestic adoption and you cannot get an SSN yet, or if the child is a foreign national who already has permanent resident status and still needs an ATIN for filing. Timing matters. Apply as soon as you are eligible, and aim for at least eight weeks before your return is due. Typical processing runs about four to eight weeks after the IRS receives a complete application.

If you do not see movement after eight weeks, call the Austin ATIN Unit at 737‑800‑5511. Keep copies of everything you mail, and use a trackable method.

Reporting a Child’s SSN on Form 15100

Once the adoption finalizes and the Social Security Administration issues an SSN, notify the IRS so they can retire the ATIN tied to your child. Report it on Form 15100 itself by checking the SSN-received box and writing in the assigned SSN. Until the SSN arrives, keep filing with the ATIN. After you report the SSN on Form 15100, stop using the ATIN, update any payroll or dependent records that list the ATIN, and save the confirmation for your files.

Updating IRS Records, Practical Steps

• Confirm which form applies to your case, then prepare the required documentation.
• If you receive a CP notice, match the notice number and names exactly, and follow the reply method it lists, for example fax or mail.
• Use a calendar reminder for eight weeks after you submit. If you do not receive a response by then, call the Austin ATIN Unit at 737‑800‑5511.
• Keep organized copies of every page you submit and any confirmations you receive.

How to Fill Out Form 15100, Step‑by‑Step

Before you put pen to paper, check that your ATIN is still active and within the window shown on your CP notice. Form 15100 is only for extending an existing, unexpired ATIN when the adoption is not yet final.

Eligibility Checklist

• You hold an active ATIN that is approaching its two‑year expiration.
• The adoption is still pending, so you cannot yet obtain an SSN.
• You can still claim the child as a dependent, or you meet eligibility for related credits.
• You received a CP notice that includes Form 15100 and a response deadline.

If your ATIN has already expired, do not submit 15100 as a new application. Read your latest CP notice for next steps and call the Austin ATIN Unit if you need direction.

Completing Form 15100

• ATIN and names, enter the ATIN, adoptive parent names, and the child’s name exactly as they appear on your IRS records.
• Current address, list your current mailing address, and write your new address if it changed since the ATIN was issued.
• Reason for extension, provide a short, plain explanation, for example, “Court date moved to April, SSN not yet available.”
• Expected finalization date, share your best estimate if you have one, or state unknown if dates are not set.
• Signature and date, sign and date the form (both adoptive parents must sign with original ink signatures, not photocopies), incomplete signatures create avoidable delays.

Keep the explanation simple and factual. One or two sentences is enough, just make it clear why an SSN is not yet available.

What to Attach and Where to Send It

• Attach the CP notice that came with Form 15100, for example CP561A or CP562C.
• Include only additional documents your notice requests, such as address evidence or SSN proof if you are reporting an SSN.
• Mail or fax to the IRS using the method and address shown on your notice. If your notice lists mail only, use the return address printed on the letter.
• Use a trackable mailing method and keep a copy of everything you send.

Mailing and Processing Timeline

Form 15100 is short, but timing is everything. You cannot file electronically through tax software. Submit the signed form promptly after the reminder arrives and before the expiration date. Plan for about eight weeks of processing. If you do not hear back by then, call 737‑800‑5511 to check status. If the deadline is close, submit immediately using the fastest method your notice allows, then keep proof of delivery.

Timing note, guidance in this article reflects procedures available as of January 15, 2026. Always follow the most recent CP notice you receive because it controls your deadline and reply method.

What Happens After You Mail Form 15100

Once your form reaches the Austin Service Center, the IRS logs your request, matches it to your ATIN record, and checks timeliness against the reminder they sent. If your submission is complete and the facts support an extension, you will receive a CP notice confirming approval and showing the new expiration date. If something is missing, they send a follow‑up asking for specific items with a response deadline.

If you receive a denial, read the reasons closely, then fix what you can, for example a missing signature or unclear explanation, and reply as instructed. If you do not receive any notice after eight weeks, call the Austin ATIN Unit at 737‑800‑5511 and have your ATIN, notice number, and mailing date handy.

Simple Status Tracker You Can Reuse

• Date you mailed or faxed the form
• Delivery confirmation number
• ATIN and notice number
• Follow‑up date set for eight weeks after submission
• Result received, approved, denied, or additional info requested

Common Mistakes and How to Avoid Them

The same handful of errors stall a Form 15100 extension, and almost all of them come from treating it like a quick checkbox exercise instead of a documented request. These are the ones worth catching before the form leaves your desk.

Printable Checklist, Form 15100 ATIN Extension

• Confirm you have an active ATIN that is nearing expiration, adoption still pending
• Gather your CP notice, ATIN, names, and current address
• Complete Form 15100 with a clear, short reason for delay and expected finalization date
• Sign and date the form
• Attach only what the notice requests
• Submit by the method and deadline in your CP letter
• Set a reminder for eight weeks, then call 737‑800‑5511 if no update
• Save copies of everything

Conclusion

Form 15100 does one thing well, it prevents an avoidable gap when an ATIN is about to expire and the adoption is still in progress. Decide which form you truly need, W‑7A to start an ATIN, or 15100 to extend it; if an SSN has been issued, report it on Form 15100 itself by checking the SSN-received box. Follow your CP notice word for word, include the essentials, sign, and submit before the deadline. Then track your status and call if eight weeks pass without an update.

Reusable Checklists

These checklists are copy-paste ready for a firm SOP. Drop them into your workpapers so anyone on the team can run a Form 15100 extension the same way every time.

Keep 15100 Season From Stalling

Form 15100 is a low-volume form with a high-stakes clock. It surfaces only when a previously assigned ATIN is close to lapsing and the adoption is still pending, so it is easy to deprioritize behind peak-season work, right up until a missed window interrupts a family's ability to file. Per the Form 15100 instructions (Rev. October 2017), the request buys one more year, and that one year is the whole point.

The fix is to treat a one-page extension with the same discipline as a full return. When the steps live in a checklist rather than someone's memory, the form moves on the first pass instead of bouncing back for a missing reason or signature.

• A standing rule that Form 15100 only extends an existing ATIN, so brand-new cases route to Form W-7A before anyone opens 15100.
• A Reason field narrative captured at intake, naming the adoptee and the previously assigned ATIN.
• A signature step that collects both adoptive parents' original-ink signatures, dates, and printed names before submission.
• A routing rule that sends USPS to the Stop 6182 P.O. box address and couriers to the Stop 6182 street address in Austin.
• A close-out trigger that checks the SSN-received box and records the SSN once it is issued, so the ATIN is retired cleanly.

When a niche form competes with high-volume work, the durable answer is to give it the same documented handling as everything else. That is what our offshore tax preparation and review teams are built for: structured SOPs, multi-layer review, and turnaround SLAs so a one-page extension never becomes the reason a filing slips.

FAQs

What documents are needed to get an ATIN in the first place?

You need Form W‑7A, placement documentation, and proof you cannot obtain an SSN yet. Send copies, not originals, and use a trackable method. If processing exceeds eight weeks, contact the Austin ATIN Unit.

Is an ATIN the same as an EIN or an ITIN?

No. An ATIN is temporary for a child in an adoption that is not final. An EIN identifies businesses. An ITIN is for individuals who are not eligible for an SSN. These numbers serve different purposes and are not interchangeable.

How long does it take to get an ATIN?

Plan for about four to eight weeks after the IRS receives a complete W‑7A package. Apply early, at least eight weeks before your return is due, and keep a copy of everything you send.

Can I e‑file Form 15100?

You cannot submit Form 15100 through tax software. Follow the reply options shown on your CP notice, for example fax or mail. The notice controls the method and deadline.

What if my ATIN already expired?

Read your latest CP notice for next steps. If you are unsure what to do, call the Austin ATIN Unit and have your ATIN, the child’s name, and any notice numbers ready.

Do I need to attach court records to extend an ATIN?

Only attach what your CP notice requests, but enclose the placement-agency or agent-signed documents that establish the pending adoption. Many extensions require the adoptee's name, the previously assigned ATIN, a short written reason for the delay, and a signed Form 15100. Extra documents can slow things down if they are not requested.

Which credits can I claim while using an ATIN?

You can generally claim eligible dependent‑related benefits that do not require an SSN, subject to the rules in effect for the year you file. Always review the current year’s instructions or work with your tax professional.