MilometryThe 24-month rule, in plain English
When a temporary workplace quietly becomes a permanent one, why the clock can start before you notice, and what it costs when it does.
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Travel to a temporary workplace is claimable. Travel to a permanent workplace is ordinary commuting and is not. The 24-month rule, which applies to employees (including directors of their own company), is one of the tests the law uses to decide which one you are looking at, and it catches people out because it works on expectation rather than hindsight.
"Claimable" here means your employer can pay you for the journey tax free up to the approved amount, and if they pay less you can claim tax relief on the shortfall against your own Income Tax (Mileage Allowance Relief).
The rule
A workplace you go to for a task of limited duration is normally temporary. It stops being temporary when your work there runs, or can reasonably be expected to run, for more than 24 months, and your attendance is for a significant part of your working time.
Both halves matter. More than two years on a site three days a week is caught. More than two years popping in once a quarter is not.
There is a sister rule: a site is also permanent if you are expected to work there for all or almost all of the time you are likely to hold the job, however short that is. That is the one that catches fixed-term and site-by-site contracts.
The part that surprises people
It is not "you can claim for the first 24 months and then stop". The test is about expectation.
If you take an assignment that everyone knows from day one will run for three years, the workplace is permanent from the first day. There is no 24 months of allowable travel followed by a cut-off. It was never temporary. That stays true even if the assignment is cut short: HMRC's own example is a 28-month posting that ended after 18, with no relief for any of it.
Conversely, if a six-month contract keeps being extended and at month 20 it becomes clear it will run past two years, the travel stops being claimable from the point the expectation changed, not from month 24. The change works the other way too: a long posting that is shortened to under 24 months becomes temporary from the date it is shortened.
That is the trap. The clock is not counting your journeys. It is measuring what could reasonably be expected at the time, judged on things like what your employer told you and the expected length of the project.
"Significant part of your working time"
The legislation does not fix a percentage, but HMRC's guidance treats 40% or more of your working time as a significant part. Below that, a workplace you attend for a limited-duration task can remain temporary even beyond 24 months. (A place you attend for an open-ended purpose is permanent however little time you spend there: the 40% test only applies to somewhere that would otherwise be temporary.)
This is what makes the occasional-visit case genuinely different from the four-days-a-week case, and why two people on the same contract can get different answers.
Four scenarios, worked through
| Situation | Temporary? | Travel claimable |
|---|---|---|
| 9-month contract, expected 9 months | Yes | Throughout |
| 3-year contract, known on day one | No | None, from day one |
| 12-month contract, extended at month 10 to 30 months | Yes, then no | Until month 10 only |
| 30-month engagement, attending one day a fortnight | Yes, if the visits are for that limited-duration task | Throughout, below the "significant part" test |
The third row is the one that costs people money, because nothing visible changes on the day the answer does.
What it is worth, in money
A 30-mile each-way drive to a site, four days a week, 46 weeks a year, at the 2026-27 approved rates for an employee's own car (55p a mile, 25p above 10,000):
| Miles | Approved amount | |
|---|---|---|
| Per day | 60 | £33.00 |
| Per week (4 days) | 240 | £132.00 |
| Per year | 11,040 | £5,760 (banded) |
£5,760 is the approved amount, not money you keep. If your employer pays you that much for the miles, it is tax free. If they pay nothing, Mileage Allowance Relief on £5,760 is worth your tax rate on it: £1,152 at 20%, £2,304 at 40%.
Why it is worth getting right
If the workplace was in fact permanent, those miles were commuting. Payments your employer made for them were taxable pay, and any relief you claimed was not due, so HMRC can recover the tax, with interest and possibly penalties. Repeated across several years, that adds up.
Getting it wrong the other way, treating a site as permanent when it qualified as temporary, means the tax-free payment or the relief goes unclaimed.
What to do about it
Keep the record either way. A journey you did not log is hard to support later if it turns out you were entitled, and a journey you logged but did not claim costs you nothing.
In Milometry, tag a genuinely permanent workplace as Workplace and your house as Home: those journeys are then recognised as ordinary commuting and kept out of your claim automatically, while staying in your records. Tag a temporary site as Business instead, and it counts.
If the status of a site changes (an extension lands, the expectation shifts), change the tag from that date. The history stays intact and the claim adjusts.
Sources
- 490: Tax and National Insurance contributions for employee travel (HMRC)
- Employment Income Manual EIM32075: temporary workplace (HMRC)
- Employment Income Manual EIM32080: the 24-month rule (HMRC)
- Employment Income Manual EIM32083: example, posting ended early (HMRC)
- Employment Income Manual EIM32084: example, posting extended (HMRC)
- Employment Income Manual EIM32086: example, below 40% of working time (HMRC)
- Employment Income Manual EIM32100: working out what the employee expects (HMRC)
- Employment Income Manual EIM32125: the fixed term appointment rule (HMRC)
- Income Tax (Earnings and Pensions) Act 2003, section 339 (legislation.gov.uk)
- Claim tax relief for your job expenses: vehicles you use for work (HMRC)
- Business travel mileage for employees' own vehicles (HMRC)
General information for UK drivers, not tax advice. The 24-month rule turns on the facts of your case: if a site is close to the line, take proper advice.
