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HMRC letter codes · Debt and payment letters (IDMS)

IDMS99Amount overdue

Last reviewed 14 October 2026 · How Tax Letters checks its facts

In short

GOV.UK says IDMS99 is a letter HMRC sends to tell you that its records show a payment is overdue.

“Letter IDMS99 … amount overdue … HMRC will contact you by letter to tell you that our records show that a payment is overdue.”

GOV.UK: Check if a letter you’ve received from HMRC is genuine · checked 14 October 2026

Information, not advice: this page reports what HMRC, GOV.UK and the bodies named publish about IDMS99. Each fact has its source and the day it was checked beside it.

What it is

HMRC’s Debt Management and Banking Manual says the wording of an IDMS99 letter varies with the type of debt.

“The wording of the IDMS99 will vary depending upon the type of debt.”

HMRC Debt Management and Banking Manual DMBM618330: Pre-enforcement: coding out: Self Assessment (SA) and Tax Credit (TC) overpayments: IDMS 99 letters · checked 14 October 2026

When HMRC sends it

HMRC’s Debt Management and Banking Manual says some Self Assessment and tax credit cases, selected for a campaign and accepted at an initial coding check, are sent an IDMS99 letter. The letter says that if payment is not made, HMRC will consider collecting the debt through PAYE, which the manual calls ‘coding out’.

“Work items for either SA or tax credits selected for a campaign and accepted at the initial coding check are sent an IDMS99 letter advising the customer that if payment is not made we will consider coding out the debt through PAYE.”

HMRC Debt Management and Banking Manual DMBM618330: Pre-enforcement: coding out: Self Assessment (SA) and Tax Credit (TC) overpayments: IDMS 99 letters · checked 14 October 2026

What it asks

GOV.UK says the IDMS99 letter will tell you how to pay and what happens if you do not pay or call HMRC within 28 days of receiving it.

“Letter IDMS99 … The letter will tell you: … how to pay … what happens if you do not pay or call us within 28 days of receiving the letter”

GOV.UK: Check if a letter you’ve received from HMRC is genuine · checked 14 October 2026

GOV.UK says of letter IDMS99: “You must not ignore this letter.”

“Letter IDMS99 … what happens if you do not pay or call us within 28 days of receiving the letter … You must not ignore this letter.”

GOV.UK: Check if a letter you’ve received from HMRC is genuine · checked 14 October 2026

GOV.UK’s page on what to do if you owe money to HMRC, which the IDMS99 QR code leads to, lists guidance on what help is available if you cannot pay your tax on time and what will happen if you do not pay your tax bill.

“Find guidance, support and information on: … what help is available if you cannot pay your tax on time … what will happen if you do not pay your tax bill”

GOV.UK: Find out what to do if you owe money to HMRC · checked 14 October 2026

Free help and HMRC contacts

GOV.UK says the QR code on letter IDMS99 takes you to its guidance and support if you owe money to HMRC for tax or penalties.

“Letter IDMS99 … The QR code on the letter takes you to our guidance and support if you owe money to HMRC for tax or penalties”

GOV.UK: Check if a QR code on a letter you’ve received from HMRC is genuine · checked 14 October 2026

GOV.UK’s page on what to do if you owe money to HMRC, which the IDMS99 QR code leads to, says that if you want to speak to someone about your debts, you can get free, confidential and independent advice from a debt adviser.

“If you want to speak to someone about your debts you can get free, confidential and independent advice from a debt adviser.”

GOV.UK: Find out what to do if you owe money to HMRC · checked 14 October 2026

Free help first

These routes are described by GOV.UK, TaxAid and Citizens Advice themselves.

  • HMRC's extra supportHMRC offers extra support if your health condition or personal circumstances make it difficult to contact HMRC, for example a mental health condition, financial hardship or being treated in hospital.
  • Someone to deal with HMRC for youYou can authorise a friend, relative or voluntary organisation to talk to HMRC for you and help you fill in forms.
  • TaxAidTaxAid helps people with tax problems who cannot pay for advice. Tax Help for Older People merged with TaxAid in July 2025.
  • Citizens AdviceCitizens Advice gives confidential advice online, over the phone and in person, for free.