Self Assessment July 31 Deadline Missed? A 2026 Bookkeeping Recovery Plan for Drivers

The Self Assessment July 31 deadline for 2025/26 has passed, but it is not too late to find out whether your payment was right. Your books now hold the answer. Halve your true 2025/26 tax bill, compare it with what you paid, and you will know whether you overpaid, underpaid or owe interest.

This guide is for the driver who missed that second instalment, or who paid a figure built on an older, staler year. It is a recovery plan, not a reminder. If your immediate problem is dealing with HMRC letters or setting up a payment plan, start with our 31 July HMRC support FAQ. Then come back here to test the numbers.

Key takeaways

• The Self Assessment July 31 deadline instalment for 2025/26 was based on your 2024/25 bill, so it may not match what you really owed for 2025/26.
• Your 2025/26 books use the 45p mileage rate. The 55p rate only starts on 6 April 2026, so it belongs in your 2026/27 forecast.
• A low payment caused by rising profit does not attract interest by itself. A claim that cut payments too far, or a missed instalment, can.
• Late payment interest on a missed instalment is limited to the amount that should have been paid, so a lower true bill can shrink the charge.
• Unpaid tax still outstanding at midnight on 2 March 2027 can attract a 5% late payment penalty.

What was the Self Assessment July 31 deadline in 2026?

It was the last date for the second payment on account towards your 2025/26 tax bill. A payment on account (POA) is an advance instalment of Income Tax and Class 4 National Insurance. HMRC normally sets each one at half of the previous year's bill, here 2024/25.

That is the weakness of the Self Assessment July 31 deadline. By the time 31 July 2026 arrived, the 2025/26 tax year had been over for almost four months. Yet the instalment still reflected the year before. Tidy books close that gap, and they do it well before the return is due.

Why might your July payment have been built on stale numbers?

Because HMRC worked it out from your 2024/25 return, not from what you earned in 2025/26. If your hours, fares, vehicle costs or business mileage changed, the instalment could be wrong in either direction. Only your 2025/26 records show the true position, which is why bookkeeping decides the next step.

Three things commonly move a driver's bill between one year and the next: hours after a car repair or new job, costs such as insurance or licence fees, and business mileage if you claim the flat rate. Our guide on bookkeeping records for your Self Assessment return explains how to capture each of these.

How do you check if your payment was too high or too low?

Close your 2025/26 books, calculate the tax on that profit, then halve the total. That half is what each instalment arguably should have been. Compare it with the figure on your HMRC statement and with the money you sent. The gap tells you which row of the decision table below applies.

1. Close the year. Total your gross takings from 6 April 2025 to 5 April 2026, using your driver app statements rather than bank payouts, so that service fees appear as an expense.
2. Fix the mileage. Check your log, then apply 45p to the first 10,000 business miles and 25p to the rest. Our guide to HMRC mileage logs and records covers what the log needs to show.
3. Add other allowable costs. Include only what your method allows. Our allowable expenses guide for drivers separates costs you can add to the flat rate from costs it already covers.
4. Estimate the bill. Take profit less your Personal Allowance, apply Income Tax, then add Class 4 National Insurance. Our driver tax calculator gives a first estimate, and your final return gives the exact figure.
5. Halve it. This is your benchmark for each 2025/26 instalment.
6. Read your statement. Sign in to your HMRC online account, choose your latest return and select 'View statements'. Note each instalment charged, each payment received and any interest.
7. Compare the three figures: benchmark, amount charged and amount paid. Then find your row in the table below.

According to HMRC's published rates, the 2025/26 Personal Allowance is £12,570, the basic rate is 20% on the next £37,700 of income, and Class 4 is 6% on profits between £12,570 and £50,270, then 2%. Scottish taxpayers have different Income Tax bands, so check GOV.UK for those. Other income, such as a part-time wage or rent, also changes the sum.

Do not mix the 45p and 55p mileage years

This is the error we most expect to see this winter. According to GOV.UK's simplified expenses rates, cars and goods vehicles get 55p for the first 10,000 miles in 2026/27, and 45p before 6 April 2026. The rate after 10,000 miles stays at 25p. So a spreadsheet updated for the new rate can quietly overstate a 2025/26 claim by up to £1,000.

The same page explains two limits. You cannot use flat rates for vehicles designed for commercial use, such as black cabs and hackney carriages. Nor can you use them for a vehicle where you have already claimed capital allowances or included its running costs as an expense. If that is you, your books should show actual costs instead.

What should you do for each result your books show?

Match your books to one of the five situations in the table. The right response depends on two questions: was your true bill higher or lower than the instalments, and did you actually pay in July? Each answer leads to a different interest position and a different action before 31 January 2027.

How interest really works on these payments

HMRC's Self Assessment legal framework manual (SALF305) makes two points that most reminders leave out. First, you are under no obligation to raise an instalment when your profit grows, so interest cannot arise on an instalment for that reason alone. Second, where instalments were missed or looked inadequate but less tax proves due, interest is only chargeable on what should have been paid.

The rate itself comes from HMRC's interest rates table. When we read it on 1 November 2026, it showed late payment interest of 7.75% and repayment interest of 2.75%, both from 9 January 2026. The rates follow the Bank of England base rate, so recheck the table on the day you calculate.

Illustrative example: a driver who missed July and then checked her books

This is an illustrative example. Farah is an invented private hire driver in England who uses the flat mileage rate on her car, has no other income and files online. All figures are ours and exist only to show the method.

Her 2024/25 profit was £34,000, which produced a bill of £5,571.80. HMRC therefore set two 2025/26 instalments of £2,785.90. She paid January 2026 on time but missed 31 July 2026. On 1 November she closes her 2025/26 books and works through the steps.

So the July charge of £2,785.90 was £1,040 more than she needed to find. If she pays £1,745.90 on 15 November 2026, that is 107 days after 31 July. At 7.75% for illustration, interest on the corrected amount is about £40, against about £63 on the full charge. We assume here that her January overpayment counts towards July.

Her statement decides the exact figure. Until she files or claims, it may keep showing the full charge.

On 31 January 2027 she then has no balancing payment for 2025/26, only a first 2026/27 instalment of £2,265.90. The second, also £2,265.90, falls due on 31 July 2027. Saving that from February to July takes about £378 a month, which is far easier than finding it in a single week.

How the 55p rate changes her next forecast

For 2026/27, Farah forecasts £48,000 of takings, £9,800 of other costs and the same 18,000 miles. The mileage claim rises to £7,500, so profit is £30,700 and the bill is £4,713.80. Without the rate rise, that bill would have been £260 higher: an extra £1,000 of deduction at 26% combined tax and Class 4.

Her two 2026/27 instalments total £4,531.80, leaving about £182 for 31 January 2028. Reducing would be pointless, because her forecast bill sits above last year's. We would also warn a driver against reducing purely because of the 55p rate. For someone at the basic rate, the gain is at most £130 per instalment, and it disappears if takings rise slightly.

Can you still reduce payments on account after 31 July?

Yes, for now. GOV.UK says you can claim up to 31 January after the end of the tax year, which for 2025/26 means 31 January 2027. You can claim online through your Self Assessment account or by posting form SA303. You must state the amount you expect to owe, so finish your books first.

The details are on HMRC's SA303 claim page, which lists falling profits, higher tax relief and more tax deducted at source as valid grounds. A claim after the year has ended is far safer than one made during it, because you are reporting a known figure rather than a forecast. That is the real advantage of acting now, and of keeping your books up to date.

Do not treat the claim as a cash-flow trick. If the true bill later proves higher, HMRC charges interest on the shortfall from the original due dates. Equally, a claim on 2026/27 instalments relies on a forecast with months still to run, so wait until you have enough of the year in your books to trust it.

What should you do before 31 January 2027?

Clear any corrected July shortfall first, because interest runs daily. Then file your 2025/26 return, confirm the instalments on your statement, and decide whether any claim to reduce is still needed. Finally, budget for the balancing payment and first 2026/27 instalment, which both fall due by midnight on 31 January 2027.

Watch the calendar as well. Both 31 January 2027 (a Sunday) and 31 July 2027 (a Saturday) fall on weekends. GOV.UK says payment should then reach HMRC by the last working day before, except for Faster Payments and card payments. So choose your method early.

On penalties, HMRC's Self Assessment manual (SAM61250) says they are not applied to payments on account as such. However, any instalment still outstanding at the balancing date is included in the balancing payment that can be penalised. It also says the system does not automatically charge the penalty where a Time to Pay arrangement was agreed before the trigger date.

If your books show an overpayment, note the refund timing. GOV.UK's refund guidance warns that you may not get a refund when tax is due within the next 45 days, because it is deducted from what you owe. Counting back from 31 January, that window opens around 17 December 2026. Repayment interest, where due, generally runs from the date you paid the money or, if later, the date it fell due.

How do you prepare for the Self Assessment July 31 deadline in 2027?

Treat 31 July 2027 as a bookkeeping date. Close your 2026/27 books by June using the 55p rate, compare the forecast bill with last year's, and decide on any claim before paying. Save monthly from February so the second instalment is ready, whether or not the figure changes.

• Update your books monthly. Record takings, fees and business miles while the details are fresh, using our mileage calculator to check the claim.
• Keep a running tax pot. Move a set share of each week's profit to a separate savings account, and adjust it each quarter.
• Consider a Budget Payment Plan. GOV.UK says you can pay weekly or monthly by Direct Debit towards your next bill, but only if you are up to date with your last one. So clear the July shortfall first.
• Review at the end of April. By then 2026/27 has closed, and you have three months to test the July instalment before it falls due.

Making Tax Digital lands a week later

According to GOV.UK's Making Tax Digital guidance, qualifying income above £30,000 for 2025/26 means using the service from 6 April 2027. That threshold was £50,000 from April 2026, and it falls to £20,000 from April 2028. So the books you close this month may also decide when you join. Qualifying income is measured before expenses, so check how to work it out on GOV.UK.

HMRC's standard update period of 6 April to 5 July has a deadline of 7 August. For a driver who joins in April 2027, that first quarterly update falls one week after the 31 July 2027 payment. The update does not settle any tax, but after sending it you can see an estimate of your bill, which helps next year's check. Our Making Tax Digital guide for drivers explains the wider change.

Self Assessment July 31 deadline: common mistakes and the penalty each triggers

• Applying 55p to 2025/26 miles. This understates profit on the return. The result is tax underpaid, interest, and possible penalties for an inaccurate return if HMRC finds it.
• Ignoring the July shortfall until the return is filed. Late payment interest keeps running on the amount that should have been paid.
• Paying nothing because you expect a lower bill. Interest can still arise on the corrected amount, and tax left unpaid at midnight on 2 March 2027 can attract a 5% penalty.
• Claiming to reduce from a rough guess. If the bill turns out higher, you pay interest from the original due dates, up to the original instalment.
• Using bank payouts as takings. Your income and fees are both understated, and your Making Tax Digital test may be wrong as well. An inaccurate return can lead to penalties.
• Delaying the return because you cannot pay. This adds a £100 late filing penalty from 1 February 2027 to whatever you owe.

Key terms

• Payment on account (POA): an advance instalment towards your next bill, due on 31 January and 31 July.
• Balancing payment: the tax still owed for a year after your instalments, due the following 31 January.
• SA303: HMRC's form for claiming to reduce payments on account, also available as an online option.
• Class 4 National Insurance contributions (NIC): the profit-based contribution paid by self-employed people through Self Assessment.
• Making Tax Digital (MTD): HMRC's system of digital records and quarterly updates for qualifying sole traders and landlords.
• Unique Taxpayer Reference (UTR): your 10-digit Self Assessment reference, used when you pay or claim.

How UK Driver Accountants helps

We are accountants for drivers only, on fixed fees from £20 a month, and independent of any ride-hailing app. Our driver bookkeeping service keeps your takings, fees and mileage current, so you can check the Self Assessment July 31 deadline figure before it falls due rather than months afterwards. See our fixed-fee pricing for what is included.

If you are catching up now, we can close your 2025/26 books, review your statement line by line and prepare your return. Where CIS work is part of your income, our 31 July guide for CIS clients explains how deductions change the sums.

Your next step

Missing the Self Assessment July 31 deadline is fixable, and the fix starts with your books rather than with a payment plan. Close 2025/26 this month, test the instalment and clear what you really owe before interest builds further. If you would like us to check the figures, contact UK Driver Accountants and send us your latest statement.

Last reviewed 1 November 2026 by the UK Driver Accountants tax team

This article is general information and not personal tax advice. Figures in the illustrative example are invented, and your own position may differ. Speak to a qualified accountant before acting. Where an HMRC dispute or penalty is involved, we recommend professional representation.