HMRC Workplace Rules · 2026/27
The 24-Month Rule: When Your Regular Site Stops Being a Temporary Workplace
Most CIS subcontractors know they can claim travel expenses to site. Far fewer know there's a time limit on that claim — and that the clock can start from the day they sign the contract, not the day they've been there two years.
Travel expenses are one of the most consistently claimed deductions for CIS subcontractors — and one of the most frequently challenged by HMRC. The 24-month rule is the reason why. It's not complicated once you understand it, but most subcontractors only find out it exists when they're facing a backdated tax bill for expenses they thought were legitimate.
What the 24-Month Rule Actually Says
HMRC defines a workplace as temporary if you attend it for a limited duration or a temporary purpose. Travel costs to a temporary workplace are an allowable business expense. Travel costs to a permanent workplace are not — they're treated the same as a regular employee commuting to their office.
A workplace becomes permanent — and loses its temporary status — when two conditions are both met:
- You have spent, or are expected to spend, more than 24 months at that site, and
- You spend more than 40% of your total working time there
Both conditions need to be met. If you're at a site for three years but it only ever represented 30% of your total working time across multiple sites, it may still qualify as temporary. If you're at a single site full-time but only for 18 months, it's temporary throughout.
The 24-month rule isn't about when you've been somewhere for two years. It's about when you expect to be somewhere for more than two years. That's the moment the site becomes permanent — not the month you cross the line.
CIS Tax Insights · 2026The Expectation Problem — Why the Clock Starts Early
This is the part that catches most subcontractors off guard. The rule applies from the point where it becomes clear that the arrangement will exceed 24 months — not from the point where it actually does.
There are three common situations:
If you sign a 30-month contract at a site, the site is a permanent workplace from day one. You cannot claim travel expenses for any part of the engagement, because the expectation of exceeding 24 months existed before you started.
If you start on a 12-month contract and it gets extended to 30 months, the site becomes permanent the day the extension is agreed — not when you reach month 24. You can claim travel for the first 12 months. The moment the extension is signed, the site is reclassified and travel claims stop.
A 15-month contract at a single site, with no expectation of extension, remains a temporary workplace throughout. Travel expenses are claimable for the full duration. If the contract later extends beyond 24 months, the site becomes permanent from the date that extension is confirmed.
What This Costs in Real Numbers
Here's a realistic comparison for a subcontractor travelling 40 miles round-trip, five days a week, at the current 2026/27 HMRC approved mileage rate of 55p per mile.
| Scenario | Annual Mileage Claim | Tax Saved (20%) |
|---|---|---|
| 15-month contract — temporary workplace throughout | ~£7,150 | ~£1,430 |
| 30-month contract — permanent workplace from day one | £0 | £0 |
| 12-month contract extended to 30 months — travel claimed throughout (incorrect) | £7,150 claimed | HMRC clawback + penalties |
| Annual value of correctly identifying temporary workplace status | Up to £1,430 per year | |
The third row in the table is the most expensive outcome. A subcontractor who continues claiming travel after a contract is extended beyond 24 months isn't just missing out on future claims — they're creating a backdated liability for claims already made, plus potential penalties for careless error.
If HMRC determines that you've been claiming travel expenses for a site that should have been classified as permanent, they can require repayment of the tax relief already claimed — plus interest from the original due date plus a penalty for careless inaccuracy of up to 30%. On two years of incorrect travel claims, this can easily exceed £3,000 in combined liability.
The 40% Rule — and Why Working Elsewhere Doesn't Always Help
Some subcontractors assume they can avoid the 24-month rule by occasionally working on other sites — effectively reducing the percentage of time spent at the main site below 40%. This can work, but it requires genuine and significant work elsewhere, not just occasional visits to another location.
HMRC looks at the proportion of your total working time at the site over the course of the engagement. Working one day a week elsewhere while spending four days at the same site means the main site still represents 80% of your working time — well above the 40% threshold. The clock keeps running.
There's also a geographic trap: if you move to a new site that is in substantially the same location as the old one — meaning the journey is essentially the same — HMRC may treat the two sites as a single workplace for the purposes of the 24-month rule. A new project on the same business park doesn't necessarily reset anything.
What to Do With Every New Contract
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Check the Contract Duration Before You Start Before accepting a new contract, confirm the expected duration. If it's under 24 months and you won't be spending more than 40% of your total working time there, travel expenses are claimable from day one. If it's over 24 months, or you're unsure, assume the site may be permanent and take advice before making claims.
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Monitor Contract Extensions Carefully When a contract is extended, work out immediately whether the total duration now exceeds 24 months. If it does, stop claiming travel expenses from the date the extension was agreed — not from when you hit month 24. Keep a note of the extension date in your records.
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Keep a Site Duration Log For every site you work on, note the start date, the expected end date, the contract duration, and any extensions. A simple spreadsheet with one row per site tells you at a glance which sites are approaching the 24-month threshold and which have already crossed it.
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Track Your Time Across Multiple Sites If you work across several sites simultaneously, keep a log of days spent at each. This lets you demonstrate that no single site exceeds 40% of your total working time — which is the other condition HMRC applies. Without records, any claim HMRC challenges is much harder to defend.
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Take Advice Before a Long Contract Starts — Not After If you're considering a contract that might last 24 months or more, speak to your accountant before accepting it. They can confirm whether it's likely to trigger the permanent workplace rule and structure your engagement in a way that protects as much of your travel claim as possible. The cost of a brief consultation is small compared to a backdated clawback.
Frequently Asked Questions
Does the 24-month rule apply if I'm a sole trader or only to employees?
The 24-month rule applies to both employees and self-employed sole traders. For CIS subcontractors operating as sole traders, the rule determines whether travel to a site is an allowable business expense on your Self Assessment return. The same two tests apply: duration over 24 months, and more than 40% of working time at the site.
What expenses can I no longer claim once a site becomes permanent?
Once a site is classified as a permanent workplace, you can no longer claim: travel costs to and from that site (mileage, fuel, public transport); accommodation costs for nights away related to that site; or subsistence expenses (meals) for days at that site. You can still claim other legitimate business expenses unrelated to travel to that specific site.
Can I claim travel expenses to a site while waiting to find out if a contract will be extended?
Yes — while the expected duration remains under 24 months, travel claims are valid. If you're on a 12-month contract with no confirmed extension, claim normally. The moment an extension is confirmed that takes the total over 24 months, stop claiming from that date. Keep documentation of when extensions were agreed so you can demonstrate the point at which your claims stopped.
Does starting a new contract at the same site reset the 24-month clock?
Not automatically. HMRC looks at the continuity of the attendance at a location rather than just the contract structure. If you finish one contract at a site and immediately start a new one at the same location, the clock generally continues rather than resets. A genuine break in attendance at the site — typically several months — may reset the position, but this depends on the specific facts. Speak to your accountant if this situation applies to you.
People Also Ask
When does the 24-month rule apply to CIS subcontractors?
The 24-month rule applies when you spend, or are expected to spend, more than 24 months at the same workplace AND more than 40% of your working time there. When both conditions are met, HMRC reclassifies the site as a permanent workplace and you lose the right to claim travel and subsistence expenses from that point.
Does the 24-month rule apply from when the contract is signed or when I reach 24 months?
From when the expectation is established — not when you physically reach 24 months. If you sign a 30-month contract, the site is a permanent workplace from day one. If a 12-month contract is extended to 30 months, the site becomes permanent the day the extension is agreed, not when you reach month 24.
Can I avoid the 24-month rule by working one day a week somewhere else?
Not reliably. The 40% rule means the site must represent less than 40% of your total working time. Working elsewhere for one or two days a week while spending the majority of your time at the same site does not reset the clock — if that site remains your primary place of work, it still counts toward the 24-month limit.
What expenses can I no longer claim once a site becomes a permanent workplace?
Once a site is classified as a permanent workplace, you can no longer claim travel costs to and from that site, fuel costs for the journey, mileage at the approved rate, or accommodation and subsistence. You can still claim other legitimate business expenses unrelated to travel to that specific site.
Know the Rule Before You Sign the Contract
The 24-month rule is one of those areas of tax law where the cost of not knowing it significantly exceeds the cost of understanding it. A few minutes reviewing the expected duration of a new contract, against the two HMRC tests, can protect years of legitimate travel claims — or prevent years of claims that would eventually need to be repaid.
Check every new contract before you start. Monitor extensions the moment they're agreed. Keep a site log. And if you're looking at a contract that's likely to run beyond two years, take advice before you accept it rather than after HMRC asks the question.
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This article is for informational purposes only and does not constitute formal accounting, legal, or tax advice. The 24-month rule and temporary workplace status depend on the specific facts of each engagement. Always consult a qualified accountant before making or stopping travel expense claims. Aligned to 2026/27 HMRC guidance.