How do Self Assessment payments work in the UK?
Self Assessment payments can feel confusing because the amount due is not always just last year’s tax. Your bill may include a balancing payment for the tax year that has ended, plus payments on account towards the next tax year. That is why many people open their HMRC account in January and see a figure that feels much higher than expected. This guide explains how Self Assessment payments work in plain English, why January and July matter, what a balancing payment means, how payments on account are calculated, and how to use a calculator to estimate what might be due before the deadline arrives.
Important information
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Who this guide applies to
- Self Assessment taxpayers
- sole traders
- freelancers
- landlords
- side hustlers
- people with untaxed income
- people making payments on account
Common costs to consider
- business software
- professional fees
- platform fees
- travel and mileage
- phone and internet costs
- stock or materials
- property expenses
- advertising
What is a Self Assessment payment?
A Self Assessment payment is the tax you pay after completing a Self Assessment tax return. It can cover Income Tax, National Insurance, student loan repayments, High Income Child Benefit Charge or other amounts depending on your situation. People often use Self Assessment when they are self-employed, work as sole traders, earn rental income, receive untaxed income, have a side hustle above the reporting threshold, earn creator income, sell online as a trade or need to report other income that has not already been taxed through PAYE. Unlike PAYE, where tax is usually taken from wages before you receive them, Self Assessment often means you receive income first and pay tax later. This makes planning important. If you spend all of your income as it arrives, the bill can feel painful when HMRC asks for payment.
The two main parts: balancing payment and payments on account
The easiest way to understand Self Assessment is to split the bill into two parts. First, there may be a balancing payment. This is the amount still owed for the tax year you have just reported. For example, if your tax return shows that you owe £4,000 for the year and you have already paid £1,000 towards it, your balancing payment may be £3,000. Second, there may be payments on account. These are advance payments towards the next tax year. HMRC uses them because many Self Assessment taxpayers do not have tax deducted at source. Payments on account are designed to spread future tax into two instalments, usually due in January and July. The confusion happens because the first payment on account is often due at the same time as the balancing payment, which can make the January bill look bigger than expected.
Why the January Self Assessment bill can feel so high
January is the month that catches many sole traders, landlords and side hustlers by surprise. By 31 January, you may need to pay any balancing payment for the previous tax year and the first payment on account for the current tax year. Imagine your completed tax return shows a £6,000 bill for the year. If payments on account apply, HMRC may ask for the £6,000 balancing payment plus a first payment on account towards the following year. A simplified example could mean £6,000 plus £3,000, creating a January payment of £9,000. Then a second payment on account may be due by 31 July. The total is not a penalty or an extra tax rate; it is partly catching up for the year just reported and partly prepaying the next one. But if you were expecting to pay only the tax from last year, it can feel like a shock.
What are payments on account?
Payments on account are advance payments towards your next Self Assessment tax bill. They are usually based on the previous year’s tax bill. In broad terms, each payment on account is usually half of the previous year’s relevant Self Assessment tax. One payment is normally due by 31 January and the second by 31 July. If your income is steady, this system can make sense because it spreads the cost. If your income drops, the payments can feel too high. If your income rises, the payments can feel too low and you may still have a balancing payment later. Payments on account are not the same as monthly PAYE deductions. They are estimate-based advance payments, and the final position is corrected when the next tax return is filed.
Who usually has to make payments on account?
Payments on account commonly affect sole traders, freelancers, landlords and people with significant untaxed income. They can also affect creators, resellers and digital product sellers once income grows. There are exceptions and detailed rules, so you should check HMRC guidance for your exact position. As a practical rule of thumb, if Self Assessment is becoming a regular part of your finances, it is worth assuming that payments on account might matter and checking early. The people most likely to be surprised are those filing for the first time after a strong year of self-employed or rental income. The first year can feel like paying one year late and one year early at the same time. That is why estimating your bill before January is so useful.
Real-world example: a freelance designer
Imagine Sam is a freelance designer. In the 2025/26 tax year, Sam makes £38,000 of business income and has £6,000 of allowable expenses. The estimated profit is £32,000. Sam has not paid tax on that profit through PAYE because the income came from clients. When Sam files the Self Assessment return, the calculation shows a tax and National Insurance bill. If this is the first year the Self Assessment bill is high enough for payments on account to apply, Sam may need to pay the balancing payment for 2025/26 plus the first payment on account towards 2026/27 by 31 January 2027. A second payment on account may then be due by 31 July 2027. If Sam only saved enough for the balancing payment, the payment on account can feel like a nasty surprise. If Sam used a calculator during the year, the shock would be much smaller.
Real-world example: a landlord with rental income
Now imagine Amira owns a rental property and receives rent each month. Her letting agent deducts fees before paying her, and she also pays insurance, repairs and mortgage interest. If Amira only looks at the net cash landing in her bank account, she may not understand her actual rental income and allowable costs. When she completes her Self Assessment return, the rental profit is added to her other taxable income. If the resulting tax bill is large enough and payments on account apply, she may face a January payment larger than expected. Landlords often need to plan carefully because property income can interact with employment income, finance cost rules and other allowances. A rental income calculator can help estimate the property element, while a Self Assessment payment calculator helps think about the payment timing.
Can payments on account be reduced?
If you genuinely expect your tax bill for the next year to be lower, you may be able to ask HMRC to reduce your payments on account. This can be useful if your self-employed income drops, you stop trading, lose a major client, sell a rental property or move income into PAYE. However, reducing payments too far can create problems later. If the reduction is too low and you still owe tax, you may need to pay the shortfall and could face interest. The safest approach is to base any reduction on realistic figures, not wishful thinking. Use actual year-to-date income, expected expenses, likely profit and known changes. If the amounts are large, it is sensible to speak to an accountant before reducing payments.
How to estimate your Self Assessment payment
To estimate your Self Assessment payment, start by estimating your taxable income for the year. For sole traders, use gross income minus allowable expenses. For landlords, use rental income minus allowable property expenses, while treating finance costs carefully. For creators and resellers, include platform income, sponsorships, sales, affiliate payments and other trading income. Then include PAYE income, tax already deducted, student loan details and other relevant income if the calculator asks for them. A Self Assessment payment calculator can estimate the balancing payment and help you think about what might be due. A payments on account calculator can then show how future instalments may be split. These tools are not a replacement for a tax return, but they are very useful for planning.
How much should you set aside for Self Assessment?
There is no single percentage that works for everyone because tax depends on profit, other income, allowances, National Insurance and personal circumstances. However, many sole traders and side hustlers use a tax pot habit. Each time they receive business income, they transfer a percentage into a separate savings account. The right percentage depends on your likely tax band and profit level. If your PAYE job already uses your Personal Allowance, your side income may be taxed more heavily than expected. If your business has high expenses, your profit may be much lower than sales. The key habit is not the exact percentage; it is separating tax money before it becomes everyday spending. Recalculate through the year as income changes.
Common Self Assessment payment mistakes
Common mistakes include saving for Income Tax but forgetting National Insurance, assuming payments on account are a penalty, looking only at net bank deposits, missing platform fees, ignoring PAYE income, forgetting student loan repayments and leaving the calculation until January. Another common mistake is thinking a tax return submitted early means payment is due immediately. Filing early can actually be helpful because it tells you what is due before the deadline. You can then plan, save, ask questions and avoid last-minute panic. Self Assessment is much easier when treated as an annual planning cycle rather than a once-a-year emergency.
Which calculator should you use?
Use the Self Assessment Payment Calculator if you want to estimate what may be due after completing a tax return, including the idea of a balancing payment. Use the Payments on Account Calculator if you specifically want to understand the January and July instalments towards the following tax year. Use the Sole Trader Tax Calculator if your main question is how much tax your self-employed profit may create. Use the Rental Income Tax Calculator if the income comes from property. These tools work best together: first estimate the income and profit, then estimate the payment timing. The final numbers should always be checked against your actual HMRC calculation, but the calculators can make the process much easier to understand.
Official references
Frequently asked questions
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