Payments on Account: Why January's Bill Is Bigger Than You Expected

What a payment on account actually is

A payment on account is an advance instalment towards next year's tax. HMRC's assumption is that if you owed a certain amount last year, you will owe something similar again, so it collects half of that in January and half in July.

It is not an extra tax. It is the same tax, collected earlier. The pain is entirely in the timing, and specifically in the first year it applies to you, when you pay a full year's tax and half of the next in one go.

The first January it applies, you pay roughly 150% of your annual bill. Every January after that is back to roughly 100%, because the previous July's instalment has already gone.

When it applies

Payments on account are due where your Self Assessment liability for the year was above a threshold, and where less than a stated proportion of your tax was already collected at source, for example through PAYE.

Both conditions matter. Someone with a large PAYE salary and modest freelance income can be over the amount threshold and still not be asked, because most of their tax was already deducted. The amounts and proportions are set by HMRC and change, so read your own Self Assessment statement rather than working from a rule of thumb.

The dates

For a tax year ending 5 April, the balancing payment for that year and the first payment on account for the next are both due on 31 January. The second payment on account follows on 31 July.

That means 31 January carries two separate amounts, which is why the total surprises people even when each part is correct.

Reducing them, and the risk

If you know your income has dropped, you can apply to reduce your payments on account. This is a genuine option and it is often the right one for someone who has gone from a strong year to a lean one.

The risk is real though: if you reduce them below what you actually end up owing, HMRC charges interest on the shortfall from the original due dates. Reducing on evidence is sensible; reducing on optimism is expensive.

How to make January boring

Set money aside as income arrives rather than working out the total in January. A running estimate of income tax and National Insurance on your actual recorded profit gives you a figure to reserve against, and the reserve is what turns a shock into an administrative task.

If the money genuinely is not there, contact HMRC about a Time to Pay arrangement before the deadline. Agreeing one before the due date generally avoids late-payment penalties, though interest still runs. Silence is the one approach that reliably makes it worse.