Millions of Self Assessment taxpayers are being warned not to miss another HMRC tax deadline this month. 

Anyone required to make a second payment on account for the 2025/26 tax year has until July 31 to pay what they owe.

HMRC is urging taxpayers to prepare ahead of the deadline, with payment options including the HMRC app, online banking and payment plans for those who are unable to pay their bill in full.

Andy Wood, tax expert at Tax Barrister UK, says many people focus solely on the January Self Assessment deadline and overlook the second payment due in July.

“January receives most of the attention, but the July payment on account regularly catches taxpayers by surprise.

“This is particularly common among people who have recently become self-employed or are filing a Self Assessment tax return for the first time. 

“They often don’t realise that tax can be paid in advance based on the previous year’s liability.”

Payments on account are advance payments towards a taxpayer’s next Self Assessment bill. 

They are generally required if a person’s previous tax bill exceeded £1,000 and less than 80% of their tax was collected through PAYE.

Failing to pay by July 31 could result in HMRC charging interest on any outstanding balance until the amount is settled.

Taxpayers whose income has fallen since the previous tax year should review whether their payment on account still reflects their circumstances, according to Wood. 

“If your profits have reduced significantly, it may be possible to apply to reduce your payment on account. However, this should only be done where there is a genuine basis for doing so.

“Reducing the amount without good reason could leave you with a larger tax bill and additional interest later, so it’s important to understand your position before making any changes.”

HMRC also offers Time to Pay arrangements for eligible taxpayers who are unable to pay their bill immediately, allowing some people to spread the cost over time.

Wood added: “One of the biggest mistakes people make is leaving everything until the final few days before the deadline. 

“If there’s an issue with your calculation or you need to arrange a payment plan, you may find yourself under unnecessary pressure.

“Keeping your records up to date throughout the year makes meeting tax deadlines much easier and helps avoid unexpected bills.”

The 31 July deadline only applies to taxpayers who are required to make a second payment on account. 

Anyone unsure whether it applies to them should check their latest Self Assessment statement through their HMRC online account or seek professional advice before the deadline.