Somewhere in a spare bedroom turned office in Leeds, a freelance graphic designer is staring at her HMRC app, wondering why there's a fresh bill for £2,140 sitting in her account six months after she thought she'd already settled up with the taxman. She paid in January. She has the confirmation email to prove it. And yet here's a second demand, due at the end of July, for exactly half of what she paid before.
She isn't imagining it, and she isn't alone. Every year, thousands of self-employed people, small landlords and contractors get caught out by the same quirk of the Self Assessment system: payments on account. It's not a mistake, a duplicate bill or an HMRC error — it's how the system is designed to work. The trouble is that almost nobody explains it properly when you first register as self-employed, so the July bill lands like a second tax return nobody warned you about.
What a payment on account actually does
HMRC assumes, reasonably enough, that if you owed a certain amount of tax last year, you'll owe something similar this year. Rather than wait twelve months for one enormous bill, it splits your estimated liability into two advance instalments: one due on 31 January, alongside your final balancing payment for the previous tax year, and a second due on 31 July. Each instalment is worth 50% of your total Self Assessment bill from the year before — income tax and Class 4 National Insurance combined, but not capital gains tax or student loan repayments, which are excluded from the calculation.
So when our Leeds designer paid £4,280 in January, £2,140 of that was her actual bill for the previous tax year, and the other £2,140 was a payment on account towards the current year — a down payment on tax she hasn't technically finished earning yet. The July payment is the second half of that same advance. It isn't new tax. It's tax she already knew about, just poorly explained the first time round.
Who this applies to
Payments on account kick in automatically once two conditions are both true: your Self Assessment bill for the year came to more than £1,000, and less than 80% of the tax you owed was collected at source (through PAYE, for instance, if you also have a salaried job). Most sole traders, freelancers and landlords with rental income above the £1,000 property allowance fall into this bracket without ever choosing to. If your bill was under £1,000 — a small side hustle earning a few hundred pounds a year, say — you're exempt, and you simply pay whatever you owe once, by 31 January.
- First-year traders are usually spared the July payment, because there's no prior year's bill to base it on — the shock tends to arrive the second January instead, when both the balancing payment and the first payment on account land together.
- Anyone whose income is genuinely lower this year than last has a legitimate route to reduce the July bill (more on that below), though HMRC will charge interest if you get the reduction wrong.
- Company directors paying themselves mostly through PAYE and dividends often escape payments on account entirely, since a large share of their tax is already collected through the payroll.
Why the July bill blindsides so many people
The honest answer is that January eats all the attention. Every accountant, every finance forum and every HMRC reminder email is focused on the 31 January deadline, because it's the bigger, scarier one — the balancing payment plus the first instalment, often the largest single tax bill of the year. By the time that's paid, most people mentally close the folder on tax until the following spring. Nobody's diary says "put money aside for July," so nobody does.
That's the trap. The July payment is smaller in isolation, usually, but it lands at an awkward time — often overlapping with summer holiday costs, a slow trading month for seasonal businesses, or a VAT payment for anyone registered. A self-employed builder who's just paid for two weeks in Portugal and a new set of scaffold boards doesn't necessarily have £1,800 sitting spare for HMRC. Miss it, even by a few days, and the interest starts accruing from 1 August — currently calculated at the Bank of England base rate plus 2.5 percentage points, applied daily until the balance clears. Here's the part that catches people out twice. Miss the July payment and you haven't just delayed one bill — you've walked straight into the next one. The following January doesn't just bring a fresh balancing payment and a new payment on account; it brings all of that stacked on top of the July amount you never cleared, plus several months of interest. What started as a manageable £1,800 shortfall in July can easily be a four-figure demand by January, with interest compounding the whole way.
Reducing your payment on account — and where it goes wrong
If your income this year is genuinely lower than last year — you lost a major client, cut your hours, or switched from self-employment to a salaried role partway through — you can apply to reduce your payments on account rather than pay the full amount HMRC estimated. This is done through your Self Assessment account online, or by submitting form SA303, and it can be applied to either the January or July instalment, or both. Reduce it too far, though, and HMRC will charge interest on the shortfall once your actual tax bill comes in, calculated as if you'd underpaid from the original due date. Reduce it to nil when your income has actually held steady, and you're simply deferring a bill that returns with interest attached the following January — worse than paying it on time. The sensible move is to reduce the payment only when you have a genuine, evidenced reason to expect lower profits, and to base the new figure on realistic numbers, not wishful thinking about a slow year turning itself around. Freelancers who've had a rough year and know it — a graphic designer who lost her biggest retainer client in March, for instance — are usually better off reducing the payment properly through form SA303 than simply not paying and hoping nobody notices. HMRC's systems flag missed payments within weeks, not months.
The half-hour fix that actually works
The single most effective habit for self-employed people isn't a clever tax trick.
It's a separate savings account that exists purely for HMRC money, funded automatically the moment income arrives, rather than raided from the current account in a panic every January and July. Set aside 25–30% of every invoice the day it's paid — a rough blend covering income tax, Class 4 NIC and a buffer for payments on account — and by the time either deadline arrives, the money is already sitting there, untouched, earning a bit of interest in the meantime.
A number of challenger banks now offer "tax pots" or automatic savings rules built specifically around this pattern, moving a fixed percentage of every incoming payment into a locked sub-account. Whether you use one of those or just a plain second account with a different bank so it's genuinely awkward to dip into, the mechanics matter less than the discipline. Set it up once, on a slow Tuesday afternoon, and both the January and July bills stop being emergencies and start being non-events.
What to check before 31 July
Log into your HMRC online account or the app and look at the "View your Self Assessment tax return" section — the exact amount due for 31 July is listed there, not just estimated. Cross-check it against your own records if you've had a significant change in income, and file the reduction claim well before the deadline if you need one, since processing isn't instant. Pay by Direct Debit, online banking, or through the HMRC app itself; card payments through some third-party services carry a fee that a simple bank transfer doesn't.
Don't wait until the evening of 31 July to sort this out — bank transfers can take a working day to clear, and HMRC counts the payment as late if it hasn't arrived by the deadline, not merely sent by then. Set a reminder for the 25th, check the balance in the tax pot, and pay early. It's one less thing sitting in the back of your mind through August.