HMRC Mileage Rates 2026 in Cardiff: A Complete Guide to the Backdated 55p Catch-Up

HMRC mileage rates 2026 let self-employed drivers claim 55p a mile for the first 10,000 business miles and 25p for every mile after that. The rise is backdated to 6 April 2026, so every business mile you have driven around Cardiff since then qualifies for 55p, even if your records still say 45p.

The announcement came weeks into the tax year. By then, many drivers had already set up a spreadsheet, a tracking app or Making Tax Digital (MTD) software at the old rate. This guide is about that clean-up: where the old 45p is still sitting in your records, how to re-rate the same miles properly, and what it means for a Cardiff driver paying Welsh rates of Income Tax.

Key takeaways

• Under the HMRC mileage rates 2026/27, the simplified rate is 55p for the first 10,000 business miles and 25p after, applied from 6 April 2026.
• Your miles do not change. Only the rate applied to them does, so never edit the trips in your log.
• Check four places for a hidden 45p: spreadsheet formulas, app settings, MTD software and your tax set-aside plan.
• MTD quarterly updates are cumulative, so a corrected record normally flows into your next update.
• Miles driven before 6 April 2026 stay at 45p on your 2025/26 return, due online by 31 January 2027.

What is the backdated 55p catch-up?

The backdated 55p catch-up is the job of re-pricing business miles you already recorded at 45p since 6 April 2026. Your trip log stays as it is. You change the rate used in your totals, so your 2026/27 mileage deduction reflects 55p for the first 10,000 business miles.

According to HMRC's policy paper on increasing mileage rates, published 17 June 2026, the increase is retrospective and takes effect from 6 April 2026 for the 2026/27 tax year. The paper also says the government has committed to review the rates beyond 2026/27, so treat 55p as a 2026/27 figure and check again next spring.

HMRC mileage rates 2026: which rate applies to which journey?

Under the HMRC mileage rates 2026 rules, the journey date decides the rate. Business miles driven from 6 April 2026 use 55p for the first 10,000 and 25p after that. Business miles driven up to 5 April 2026 belong to 2025/26 and use 45p, then 25p. Keep the two years completely separate in your records and totals.

HMRC's simplified expenses guidance for vehicles sets out both columns side by side, which is useful if you are finishing your 2025/26 return this winter while also tidying 2026/27. We built the table below to stop the two years getting mixed up.

A night shift that runs past midnight on 5 April 2026 is the only awkward case. Split it by the time each trip ended, so the earlier trips sit in 2025/26 and the later ones in 2026/27. If you are unsure, put a note against the shift explaining how you split it.

Where is 45p still hiding in your records?

In our experience the old rate rarely sits in one place. It hides in spreadsheet formulas, app rate settings, MTD software categories and the tax set-aside plan you made in spring. Check each one, because fixing the spreadsheet alone can leave your quarterly figures or savings plan still built on 45p.

The money-cap trap

This one catches careful drivers. If your spreadsheet stops charging 55p once the claim reaches a pound amount, rather than a mile count, the band ends too early. At 45p the cap was £4,500, which matched exactly 10,000 miles. At 55p the same £4,500 is reached after about 8,182 miles, and every mile after that is wrongly priced at 25p.

The fix is to count miles, not pounds. The 10,000-mile band is about the number of business miles in the tax year. If you want a quick cross-check of your band split, run your year-to-date miles through our mileage calculator and compare its total with your spreadsheet.

How do you correct miles you logged at 45p?

You correct them by re-pricing, not rewriting. Keep every original trip entry, add up your business miles since 6 April 2026, apply 55p to the first 10,000 and 25p to the rest, and record the date you made the change. Then update any MTD software and your tax set-aside so they match.

Here is the catch-up process we use with drivers. It takes most people under an hour once their log is in one place.

1. Freeze a copy of your log as it stands today, before you change anything, and label it with the date.
2. Remove any trips dated on or before 5 April 2026 from the 2026/27 total; they belong on your 2025/26 return at 45p.
3. Add up business miles only from 6 April 2026 to today. Leave commuting and private miles out.
4. Price the first 10,000 business miles at 55p and any miles above 10,000 at 25p, using a mile-based cap.
5. Write a one-line note in the log: the date, 'rate changed from 45p to 55p per HMRC policy paper, retrospective to 6 April 2026', and the old and new totals.
6. If you are in MTD, correct the mileage figure in your digital records before your next quarterly update is due.
7. Re-run your tax set-aside with the new figure, and set a reminder to check the rate again before 6 April 2027.

If your log itself has gaps, that is a different problem. Our guide to the HMRC mileage log and how long to keep records covers what each entry needs and how to deal with missing weeks.

What if you already sent an MTD quarterly update at 45p?

You normally fix it in the next update rather than resending the old one. GOV.UK says each quarterly update runs from 6 April to the end of that quarter, and corrections to your records are included in your next update. The fourth update is the exception and may need resending.

According to HMRC's guidance on sending MTD quarterly updates, standard quarters end on 5 July, 5 October, 5 January and 5 April, with deadlines of 7 August, 7 November, 7 February and 7 May. As this guide goes live, the update for the quarter to 5 October 2026 is due on 7 November 2026. That is the natural point to put the 55p figure right.

MTD for Income Tax applies from 6 April 2026 to sole traders and landlords with qualifying income above £50,000. The threshold falls to £30,000 from April 2027 and £20,000 from April 2028. HMRC has said it will not apply penalty points for late quarterly updates in 2026/27, but late returns and late payment are still penalised. Our mileage and MTD update explains digital mileage records in more depth.

Illustrative example: a Cardiff driver's 45p clean-up

This is an illustrative example with an invented driver and our own figures. Ceri is a self-employed private hire driver licensed by Cardiff Council. Ceri set up a spreadsheet in April 2026 at 45p a mile, with a pound cap of £4,500 for the higher band. Ceri's qualifying income for 2026/27 is well under £50,000, so MTD does not apply this year.

From 6 April to 5 October 2026, Ceri logged 7,400 business miles. At 45p the spreadsheet shows £3,330. Re-priced at 55p, the same miles give £4,070, an extra £740 of deduction so far. Ceri expects about 13,500 business miles by 5 April 2027, with long airport and stadium runs in the busy months.

Changing the rate but leaving the pound cap in place would still under-claim by £545.50. Fixing both gives Ceri £1,000 more deduction than the 45p version. Ceri pays the Welsh basic rate, so that extra £1,000 reduces Income Tax by about £200, with a further, smaller saving in Class 4 National Insurance. Ceri also lowers the monthly tax set-aside to match.

Can you switch to 55p if you claim actual car costs?

Not for the same car in most cases. GOV.UK says you cannot use simplified expenses for a vehicle you have already claimed capital allowances on, or included as an expense in your profits. The rate rise does not reopen that choice. A replacement vehicle, though, gives you a fresh decision.

The same GOV.UK page also says that once you use the flat rate for a vehicle, you must stay with it while you use that vehicle in the business. So if you are about to change cars in Cardiff, compare the two methods before the new car's first business mile. Parking and other travel costs, such as train fares, can still be claimed on top of the flat rate.

What does the 55p catch-up mean for Cardiff drivers?

The mileage rate is the same across the UK, but Cardiff drivers pay Welsh rates of Income Tax on the profit that remains. That decides what each extra pound of deduction is worth. Your Cardiff Council licence renewal also involves an HMRC tax check, which is a good prompt to bring your records up to date.

According to GOV.UK's page on Welsh Income Tax, you pay Welsh rates if you live in Wales, the rates are set by the Welsh Government, and HMRC adds a C to the start of your tax code. For 2026/27 it lists 20% on income from £12,571 to £50,270, 40% to £125,140 and 45% above that. A Cardiff driver near the £50,270 line should check which band the extra deduction comes off.

Cardiff Council licenses hackney carriage and private hire drivers and vehicles. HMRC's guidance on the tax check for taxi and private hire licences says checks have applied in England and Wales since 4 April 2022, mainly on renewal, and each code expires after 120 days. The check confirms tax registration, not your mileage figure, but a tidy year makes renewal less stressful.

Cardiff work patterns matter too. Long runs to the airport or beyond, plus matchday and concert surges, can push a full-time driver past 10,000 business miles before spring. If you expect to cross the band, keep a running mile count so you know the exact date you move to 25p. Check Cardiff Council's own website for any vehicle emission or clean air conditions that affect your licence, as we do not cover those here. For more on the city, see our Cardiff driver accountant page and our guide to the 2026 update for Cardiff tax returns.

Key terms

• Simplified mileage (flat rate): a fixed amount per business mile that replaces actual running costs such as fuel, insurance and repairs.
• Business mile: a mile driven for your driving business, not commuting or private travel.
• Retrospective: applying from an earlier date than the announcement, here 6 April 2026.
• MTD (Making Tax Digital) for Income Tax: HMRC's system of digital records and quarterly updates for sole traders and landlords above the income threshold.
• Quarterly update: a cumulative summary of income and expenses sent to HMRC through MTD software.
• Capital allowances: tax relief on the cost of a vehicle or equipment, claimed instead of the flat mileage rate.
• UTR (Unique Taxpayer Reference): the 10-digit number HMRC gives you when you register for Self Assessment.

Common 45p catch-up mistakes and the penalty each can trigger

Most catch-up errors cost you money rather than triggering a penalty, because they under-claim. The risk runs the other way when 55p leaks into the wrong year. HMRC's factsheet on penalties for inaccuracies says there is no penalty if you took reasonable care. Careless errors that leave tax unpaid can cost 0% to 30% of the extra tax if you tell HMRC unprompted, and 15% to 30% if prompted.

• Using 55p for March 2026 miles on your 2025/26 return: this over-claims and can attract a careless inaccuracy penalty plus interest on the tax due.
• Editing trip dates or miles to make totals look tidier: this damages your evidence and, if done knowingly, can move a mistake into the more serious deliberate category.
• Leaving the £4,500 pound cap in your spreadsheet: no penalty, but you pay more tax than you need to.
• Updating the app but not the MTD record: your quarterly figures stay wrong until corrected, and the fourth update may need resending.
• Claiming the flat rate on a car you already claimed capital allowances on: this is not allowed and the excess claim can be treated as an inaccuracy.
• Not noting why the totals changed: no penalty in itself, but it makes any HMRC question harder to answer.

If you spot an error after filing, GOV.UK says you can correct a Self Assessment return within 12 months of the filing deadline. If HMRC has already written to you about mileage, read our guide on what to do when HMRC questions a 55p claim and get professional representation before you reply.

How UK Driver Accountants helps

We are an accountancy practice for drivers only, independent of any ride-hailing app, with fixed fees from £20 a month. Our bookkeeping service for drivers can re-price your 2026/27 mileage, check the band split and line up your MTD records. Our personal tax service then files the return at the right rates for each year.

You can see what each plan includes on our pricing page. If you are deciding whether to bring in help this year, our step-by-step guide to hiring a Cardiff private hire accountant and our page on what Cardiff drivers can do in their HMRC account cover the practical side.

Fix the 45p before the year closes

Under the HMRC mileage rates 2026 changes, 55p is already yours for every business mile since 6 April 2026. The work is making your spreadsheet, app, MTD software and savings plan agree with it, without touching the trips themselves. Do it now, while April's journeys are still easy to check. If you would like us to look over your figures, contact us for a fixed-fee quote.

Last reviewed 6 November 2026 by the UK Driver Accountants tax team

This article is general information and not personal tax advice. Rates and rules can change, so check GOV.UK and speak to a qualified accountant about your own situation. Where HMRC has opened a check, dispute or penalty, we recommend professional representation.