TL;DR
- A STAC (Service Termination Authorisation Code) lets you leave a mobile operator without carrying your number to a new network.
- Requesting a STAC cancels your service; your number returns to the operator's pool and is eventually reallocated by Ofcom rules.
- Operators must provide a STAC within one working day of a valid request, under the General Conditions of Entitlement.
- You have a brief window — typically up to 30 days while the code is valid — to reconsider before the number is formally released.
- If you want to keep your number, a PAC (Porting Authorisation Code) is the correct route instead of a STAC.
What a STAC is and why it exists
Mobile number portability in the UK operates through a dual-code system regulated under Ofcom's General Conditions of Entitlement. The PAC (Porting Authorisation Code) enables number transfer between operators; the STAC handles the mirror situation — customers who want to terminate service entirely without transferring their number. The STAC was introduced partly to streamline clean exits and to give consumers a formal, time-limited mechanism that operators must honour promptly.
Before the standardised code system, leaving a network without porting involved variable cancellation procedures and inconsistent timelines across operators. Ofcom's reforms, which came into force in July 2019, required all operators to issue both PAC and STAC codes within one working day of a valid request, and to provide them by text message or other immediate electronic means wherever possible. This removed the practice of lengthy phone-based retention conversations as a prerequisite to cancellation.
How to request a STAC
The quickest route is to text “STAC” to 75075. The operator is required to respond within one working day with the code itself, your termination date, and any relevant outstanding balance or early termination charge information. Some operators also accept STAC requests via their app, web account, or customer services telephone line, though the text route is the mandated minimum standard.
When you receive the STAC, note the expiry date on the response message. Codes are typically valid for 30 days. If you do nothing with the code, your contract continues as normal and the code simply lapses — you are not automatically terminated by requesting one. This gives you a meaningful window to compare alternatives, check any early termination fees, and confirm you genuinely want to leave without porting.
What happens to your number after a STAC is used
When a STAC is acted upon — meaning you complete termination rather than let the code expire — your mobile number is returned to your operator's number range. Under the UK National Telephone Numbering Plan, administered by Ofcom, operators are required to return unused numbers to Ofcom's central numbering pool after a quarantine period, at which point they become available for reallocation. The precise timing before a number is reassigned to another subscriber varies by operator, but the number should be considered gone within a matter of months rather than years.
There is no mechanism to “reserve” a number while it sits in the pool. Once it re-enters circulation, any subscriber on any network could be assigned it. If you later regret losing the number, recovery is not guaranteed and in most cases not possible. This is why Ofcom's guidance encourages consumers to consider whether they actually need portability before requesting a STAC rather than a PAC.
STAC process and implications at a glance
| Stage | What happens | Timeframe | Consumer note |
|---|---|---|---|
| Request STAC (text 75075) | Operator receives termination intent | Immediate | No commitment yet; code not yet issued |
| Operator issues STAC | Code sent with expiry and ETF details | Within 1 working day | Check any early termination charge shown |
| Code validity window | Contract continues; code can lapse unused | Typically 30 days | Safe period to reconsider |
| Termination completes | Service cancelled; number returned to operator pool | On confirmed exit date | Settle final bill; remove SIM |
| Number in quarantine pool | Operator holds number before returning to Ofcom pool | Weeks to months (operator-dependent) | Number not yet reassigned but not recoverable |
| Number reallocated | Enters general circulation via Ofcom numbering plan | Months after release | Number permanently gone |
Alternatives before committing to a STAC
Before requesting a STAC, it is worth working through a short checklist. If the reason for leaving is cost, operators are under Ofcom's Fairness for Customers commitments to make accessible any lower tariffs available to new customers, and many will offer retention deals not publicly advertised. If the concern is a change in personal circumstances — such as reduced income — some operators offer payment deferrals or social tariffs; see their vulnerability support policies. If the problem is service quality, Ofcom complaints rights apply.
If you want to move to another UK network but keep your number, a PAC (text “PAC” to 65075) is the correct code. A PAC triggers a smooth transfer rather than a termination, and the old contract closes automatically once the port completes. Requesting a STAC when you intended a PAC is one of the more common errors consumers make, and it results in an avoidable loss of a number. If you are undecided, do nothing after receiving the STAC — the code will lapse and your service continues.
Early termination charges and the STAC
A STAC does not waive any early termination fee (ETF) payable under the contract. Ofcom rules permit operators to charge reasonable ETFs when customers leave before the minimum term ends, subject to the requirement that those charges reflect only the genuine loss to the operator (primarily the outstanding line rental) rather than acting as a penalty. The STAC response message from the operator must state any ETF that will apply, so consumers can factor this into the decision.
In practice, if you are in the final one or two months of a contract, many operators choose not to enforce an ETF. If you are mid-contract, the charge can be substantial. Consumers who believe an ETF is disproportionate can raise this through the operator's complaints process and, if unresolved, refer to an Ofcom-approved alternative dispute resolution (ADR) scheme — either Ombudsman Services: Communications or the Communications and Internet Services Adjudication Scheme (CISAS).
What this means in practice
Priya, based in Birmingham, is eight months into a 24-month SIM-only contract. She decides to switch to a SIM from a family member's account on a different network and does not need her current number, which she has only had for a year. She texts “STAC” to 75075 and receives a code the following morning along with notification of a remaining contract balance of roughly £80 in line rental. She checks the operator's retention page but finds no matching tariff. She uses the STAC, pays the ETF, and closes the account. Three months later a different subscriber on a different network is allocated her old number. Had Priya wanted to keep the number she would have needed to text “PAC” instead — a common point of confusion that Ofcom has noted in consumer research.
Related Guides
How we verified this
This article draws on Ofcom's General Conditions of Entitlement (General Condition C8, number portability and switching), Ofcom's July 2019 switching reforms guidance, the UK National Telephone Numbering Plan published by Ofcom, and Ofcom's Fairness for Customers programme documentation. No operator-specific pricing or statistics are presented.
Disclaimer: Kaeltripton.com is an independent UK editorial publisher. We are not regulated by Ofcom or the FCA and we do not sell or arrange mobile services, insurance, or financial products. This content is for general information only and is not legal, financial, or technical advice. Rules, prices, and operator policies change. Verify the current position with Ofcom, GOV.UK, the ICO, or your provider before acting. ICO registered ZC135439. Last reviewed: 2026-06-05.
Frequently Asked Questions
How do I cancel my mobile without taking my number?
Text “STAC” to 75075 from the number you want to cancel. Your operator must respond within one working day with a Service Termination Authorisation Code. Using that code terminates your contract and relinquishes your number. If you let the code expire without acting, your service continues unchanged. Do not use a STAC if you want to keep the number — request a PAC instead.
What is a STAC code?
A STAC (Service Termination Authorisation Code) is a unique alphanumeric code your mobile operator must supply within one working day of a valid request. It formally authorises the termination of your mobile service without number portability. The code was standardised under Ofcom's 2019 switching reforms to make clean exits simpler and faster for consumers.
How do I get a STAC code?
The simplest method is to text the word “STAC” to 75075 from the mobile number you wish to cancel. Ofcom requires operators to respond within one working day. Many operators also accept STAC requests through their app, online account portal, or customer services line. The response must include the code, its expiry date, and details of any early termination charge that applies.
What happens to my number when I use a STAC code?
Your number returns to your operator's internal pool when the termination completes. After a quarantine period — which varies by operator but is typically measured in weeks to months — the number is returned to Ofcom's central numbering plan and becomes available for reallocation to any subscriber on any network. Once reallocated, recovery is not possible.
Can I change my mind after using a STAC code?
You can change your mind while the code is still in its validity window and has not yet been acted upon — simply do nothing and the code lapses, leaving your contract active. Once termination has completed, reversing it is at the operator's sole discretion and is not guaranteed. Act quickly if you reconsider; contact customer services immediately and ask whether reinstatement is possible.
