Self Tax Assessment in Newcastle: Step-by-Step When You Sell or Swap Your Car

If you claim actual car costs and sell or part-exchange your car mid-year, your self tax assessment has to close that car's capital allowance pool. You compare what you got for the car with its remaining tax value, then claim a balancing allowance or report a balancing charge, reduced by your private use share. You cannot avoid the calculation by switching that car to the mileage rate.

This guide is for Newcastle private hire and ride-hailing drivers who claim real running costs and capital allowances rather than the flat mileage rate. It walks through the 2026/27 rules in the order you would actually do the work: find the pool, apply the right rate, deal with the sale, adjust for private use, then fill in the return. If you use the flat rate instead, our mileage rate FAQ for Newcastle drivers changing car covers that route, and we do not repeat it here.

Key takeaways

• A car you also use privately sits in its own single asset pool, so selling it always puts a balancing figure on that year's self tax assessment.
• Sale price below the pool balance gives a balancing allowance; sale price above it gives a balancing charge. Both are cut to your business use share.
• From 6 April 2026 the main rate writing down allowance is 14% (it was 18%), and the special rate stays at 6%. CO2 emissions decide which applies.
• A car you have claimed capital allowances on can never move to the 55p mileage rate. Your replacement car gets a fresh choice.
• New, unused zero-emission cars can still get a 100% first-year allowance if bought by 5 April 2027 for Income Tax purposes.

What is a self tax assessment?

A self tax assessment is the annual Self Assessment tax return you file with HMRC as a self-employed driver. You report your fares, your allowable costs and your capital allowances, and HMRC works out the Income Tax and National Insurance due on the profit for the tax year.

Key terms

• Capital allowances: tax relief on the cost of a business asset such as a car, given over several years instead of as one expense.
• Pool: a running record of the tax value of an asset or group of assets. You add costs, deduct sale proceeds and claim allowances from it.
• Single asset pool: a separate pool for one item you also use privately, such as your car.
• Writing down allowance (WDA): the yearly percentage you can claim on a pool balance, 14% main rate or 6% special rate in 2026/27.
• First-year allowance (FYA): an allowance claimed in the year of purchase. New zero-emission cars currently get 100%.
• Tax written down value (TWDV): what is left in the pool after allowances. This is the figure you compare with the sale price.
• Balancing allowance or charge: the final adjustment when the car leaves the business, giving extra relief or adding taxable profit.

Who is this self tax assessment guide for?

It is for self-employed drivers who claim actual vehicle costs, such as fuel, insurance and repairs plus capital allowances on the car, and who sold, part-exchanged, scrapped or stopped using that car during the year. If you claim the flat mileage rate, none of the pool steps below apply to you.

Most drivers who end up in this position chose actual costs years ago, often for a newer or more expensive car, and have carried the pool forward since. The sale is the moment the pool is settled. Get it wrong on your self tax assessment and you either lose relief you were owed or under-report profit, which HMRC can correct with interest.

Why can't you switch the old car to the mileage rate?

Because the choice of method is tied to the vehicle. GOV.UK states that you cannot use simplified expenses for a vehicle you have already claimed capital allowances on. Once a car has been on actual costs, it stays there until it leaves your business, and its sale must be dealt with through its capital allowance pool.

According to GOV.UK's simplified expenses guidance for vehicles, the 2026/27 flat rate is 55p a mile for the first 10,000 business miles, then 25p, with 45p applying before 6 April 2026. Those figures matter only for your next car. HMRC's Business Income Manual at BIM75005 explains that a business can only move to or from actual costs when a vehicle is replaced. So the replacement is your one chance to choose again, and the outgoing car settles on the basis it has always used.

Which capital allowance rate applies to your car in 2026/27?

It depends on when you bought the car and its CO2 emissions. For cars bought from April 2021, a car at 50g/km or less (or a second-hand electric car) gets the main rate, now 14%. A car above 50g/km gets the special rate of 6%. New, unused zero-emission cars can qualify for 100%.

According to GOV.UK's guidance on capital allowances for business cars, the main rate is 14% of the car's value each year, or 18% before April 2026, and the change starts on 6 April for Income Tax businesses. The special rate is 6%. Cars bought before April 2021 use older CO2 thresholds, which the same page lists by purchase date, so check the band that matches your car's registration and purchase date.

The zero-emission first-year allowance was due to end in April 2026. The government's policy paper extending first-year allowances for zero-emission cars moved the end date to 5 April 2027 for Income Tax. A new electric car bought on or after 6 April 2027 would, on current rules, go into the main rate instead. Check GOV.UK before you commit, because these dates do change at Budgets.

How does private use change the numbers?

Private use does not change the pool itself. You calculate the full allowance or balancing figure first, then claim only the business share. The full allowance still comes off the pool balance, so the private part of each year's allowance is simply lost rather than carried forward.

HMRC's Capital Allowances Manual at CA27005 says the reduction must be just and reasonable, and that the balancing adjustment on disposal reflects non-business use over the whole period of ownership. In practice, your mileage logs are the evidence. If your business share was 80% one year and 70% the next, an accountant will usually weigh the reduction across the years you owned the car rather than just using the last figure. Our guide to keeping a mileage log and bookkeeping records shows what a log that stands up to questions looks like.

On your self tax assessment, running costs follow the same logic but are handled separately. Fuel, insurance, servicing and repairs are claimed at the business percentage for each car for the period you ran it. When you swap cars in September, the old car's share applies to its costs up to the sale and the new car's share applies after that.

Balancing allowance or balancing charge: which will you get?

Compare the sale proceeds with the car's tax written down value. If you sold for less, the gap is a balancing allowance that reduces your profit. If you sold for more, the excess is a balancing charge that adds to your profit. Either way, only the business use share counts on your return.

HMRC's HS252 helpsheet on capital allowances and balancing charges confirms that a balancing allowance can arise in a single asset pool whenever the asset in it is sold or disposed of. That is the key difference from the main pool, where a sale usually just reduces the balance carried forward. Use the table below to find your situation.

How do you complete a self tax assessment after selling your car, step by step?

Work through the car's history first, then the year of sale, then the self tax assessment itself. Pull last year's capital allowance working, the sale or part-exchange invoice and your mileage logs before you start. The steps below take most drivers an hour or two once the paperwork is together.

1. Find the closing pool balance for the car on last year's return. This is the tax written down value brought forward. If you cannot find it, rebuild it from the purchase price and each year's allowance.
2. Confirm the date the car left the business and what you received: the sale price, the part-exchange credit on the dealer's invoice, the insurance settlement, or the market value if you kept it.
3. Check the figure does not exceed what you paid for the car. If it does, cap it at your original cost.
4. Deduct that value from the pool balance. Do not claim a writing down allowance on the old car in the year it leaves.
5. If the result is positive, that remainder is your balancing allowance. If the sale value was larger than the balance, the difference is a balancing charge.
6. Work out your business use share from your mileage logs across the years you owned the car, and reduce the balancing figure by the private share.
7. Apportion running costs: the old car's business share for costs up to the sale, the new car's share from the day it starts work.
8. Set up the replacement car. Decide between actual costs and the mileage rate before your first claim on it, then open a new pool and a new mileage log if you stay on actual costs.
9. Enter the figures on the self-employment (full) pages of your self tax assessment, keep the working with your records, and file online by 31 January after the tax year ends.

Step 8 is where Newcastle drivers often lose money. The replacement is your one chance to change method, so run both options on realistic miles before you claim anything. Our guide to allowable expenses for ride-hailing drivers lists the running costs that sit alongside capital allowances on actual costs.

Illustrative example: a Newcastle driver who part-exchanges in September

This illustrative example uses an invented driver, Kieran, and invented figures: he drives private hire in Newcastle as a sole trader, files his own self tax assessment and draws up his accounts to 5 April. In July 2024 he bought a used petrol hybrid for £15,500. Its CO2 figure is 105g/km, so it went into a single asset pool at the special rate of 6%. His mileage logs show 80% business use in every year he owned it.

In 2026/27 Kieran's capital allowances total £31,646.64: the £3,596.64 balancing allowance on the hybrid plus £28,050.00 on the new car. Notice that the hybrid gets no writing down allowance in its final year. The balancing allowance replaces it and releases everything left in the pool, less the private share.

Now change one fact: suppose the dealer had credited £15,000 for the hybrid instead of £9,200. That beats the £13,695.80 pool balance by £1,304.20, which becomes a balancing charge. At 80% business use, Kieran adds £1,043.36 to his taxable profit. Same car, same history, opposite direction, purely because of the price.

Two more points on the new car. If Kieran had bought a second-hand electric car for the same £33,000, it would get the 14% main rate instead: £4,620.00 in the first year, of which he would claim £3,927.00 at 85%. And the 100% claim has a cost later. When he eventually sells the electric car, the pool will be nil, so most of whatever he receives will come back as a balancing charge.

Where do the figures go on the self-employment pages?

On a self tax assessment, capital allowances, balancing allowances and balancing charges go in their own boxes on the self-employment (full) pages, separate from running costs. On the 2025 to 2026 form, the balancing allowance on a sale goes in box 56 and a balancing charge in box 59. Check the current notes, as box numbers can move between years.

• Writing down allowance on a main rate car: the main rate capital allowances box (box 50 on the 2025 to 2026 form).
• Writing down allowance on a special rate car: the 6% box (box 51 on the 2025 to 2026 form).
• 100% allowance on a new zero-emission car: the zero-emission car allowance box (box 52.1 on the 2025 to 2026 form), already reduced for private use.
• Balancing allowance when you dispose of a car for less than its tax value: allowances on sale or cessation of business use (box 56).
• Balancing charge when you dispose of a car for more than its tax value: balancing charge on sales of assets (box 59).
• Fuel: HMRC's notes tell taxi and minicab drivers to put fuel in the cost of goods box (box 17), not the car and travel box. Other running costs go in car, van and travel expenses (box 20), with private use added back as disallowable.

Cash basis is now the standard way to work out profit for most sole traders, but cars are an exception: you still claim capital allowances on a car rather than deducting its price as an expense. That is why a car sale under cash basis still runs through the pool. If you use traditional accounting, the treatment of the car is the same. Our Self Assessment tax return support covers both bases.

Does Newcastle licensing affect the tax side of a car change?

Not the tax calculation itself, but it affects timing. Newcastle City Council licenses each private hire vehicle, so a replacement usually needs its own vehicle licence before it can take bookings. Days without a licensed car mean days without fares, and the date the new car starts work is the date its costs start counting.

Before you buy, ask the council's licensing team whether the car you have in mind meets its current vehicle standards, including any Clean Air Zone requirements. A car that cannot be licensed is not a business asset in any useful sense. Licence fees and vehicle tests for the new car are normal running costs at the business share. For more on driving and filing in the city, see our Newcastle driver accountant page.

What if you file under Making Tax Digital this year?

The capital allowance rules are exactly the same as on a standard self tax assessment. Making Tax Digital (MTD) for Income Tax applies from 6 April 2026 to sole traders with qualifying income above £50,000, falling to £30,000 from April 2027 and £20,000 from April 2028. You still report the sale, the balancing figure and allowances, but through MTD-compatible software.

Quarterly updates cover income and expenses as you go, and capital allowances are normally settled when you finalise the year. A mid-year car sale is a good reason to talk to your accountant before the year-end submission. Our plain-English Making Tax Digital explainer for drivers sets out who is in and when. Most drivers are still registering for Self Assessment by 5 October after the tax year they start, and filing online by 31 January, as our key tax dates for drivers summarise.

Common self tax assessment mistakes after a car sale, and the penalty each triggers

HMRC's CC/FS7a factsheet on penalties for inaccuracies says there is no penalty if you took reasonable care. A careless error can cost from 0% to 30% of the extra tax, depending on whether you tell HMRC first. Interest runs on any tax paid late.

• Carrying on writing down allowances after the sale: overclaimed relief, so the extra tax plus interest and a possible careless-error penalty.
• Leaving out a balancing charge, especially on an electric car that had 100% relief: under-reported profit, with the same exposure.
• Claiming the full balancing allowance without the private use cut: overclaimed relief that HMRC can reverse.
• Switching the outgoing car to the 55p rate for its final months: not allowed, and the mileage claim would be disallowed.
• Using a guessed sale price instead of the invoice or a supportable market value: hard to defend if HMRC opens a check.
• Forgetting to split running costs between the two cars: wrong business percentages on fuel, insurance and repairs.

If HMRC writes to you about a car claim, getting professional support with HMRC enquiries early usually keeps the matter smaller and quicker.

How UK Driver Accountants helps

We look after drivers only, on fixed fees from £20 a month, and we are independent of any ride-hailing app. For a car change, we rebuild the pool if the history is patchy, work out the balancing figure and private use cut, compare actual costs with the mileage rate for your next car, and file your self tax assessment. Our fixed-fee pricing shows what is included.

Conclusion

On a self tax assessment, selling or swapping a car you claimed on actual costs is a closing entry, not an afterthought. Find the pool balance, deduct what you received, turn the gap into a balancing allowance or charge, cut it to your business share and enter it in the right box. Then choose carefully for the next car. If you want the numbers checked before you sign at the dealer, contact UK Driver Accountants and we will run them with you.

Last reviewed 12 November 2026 by the UK Driver Accountants tax team

This article is general information on the 2026/27 rules and is not personal tax advice. Your own figures and history may change the answer, so speak to a qualified accountant before you file. If HMRC is disputing a claim or has raised a penalty, we recommend professional representation.