Late VAT Registration: Penalties and Backdated VAT 2026/27

The VAT registration threshold is GBP 90,000 of taxable turnover, measured on a rolling 12-month basis. Cross it and miss the deadline to register, and HMRC does not just wave it through. It backdates your registration, charges the VAT you should have collected, and may add a penalty. Here is what late registration actually costs in 2026/27 and how to handle it.

When you must register

You must register for VAT if either of these happens:

• Your taxable turnover over any rolling 12-month period exceeds GBP 90,000. You then have 30 days from the end of that month to register, with an effective date of the first day of the second month after you went over.
• You expect your taxable turnover to exceed GBP 90,000 in the next 30 days on its own. Here you must register by the end of that 30-day period, effective from the start of it.

The rolling test catches many growing businesses because it is not about your financial year. A strong few months can tip a rolling 12-month total over GBP 90,000 without you noticing.

What "backdated" means

If you register late, HMRC sets your effective date of registration to the date you should have registered. From that date you are treated as VAT-registered, which means:

• You owe output VAT on your standard-rated and reduced-rated sales from that date, at 20% or 5% as appropriate.
• You can reclaim input VAT on your purchases from that date, which softens the blow.
• You owe this even if you never added VAT to your invoices, because the law treats your prices as VAT-inclusive once you should have been registered.

Worked example: a missed threshold

Dev runs a design studio. His rolling 12-month turnover quietly passed GBP 90,000 and kept climbing. He should have been registered from 1 September, but only realised and registered the following 1 March, six months late.

In those six months he invoiced GBP 60,000 of standard-rated work without adding VAT. Because his prices are now treated as VAT-inclusive:

• VAT element: GBP 60,000 x 20 / 120 = GBP 10,000 of output VAT owed.
• Input VAT he can reclaim on GBP 8,000 of qualifying purchases: about GBP 1,333.
• Net VAT due to HMRC: roughly GBP 8,667, before any penalty.

Because most of his clients are consumers who will not pay extra after the fact, that GBP 8,667 comes straight out of his own margin.

The failure to notify penalty

On top of the backdated VAT, HMRC can charge a failure to notify penalty, calculated as a percentage of the VAT owed. The percentage depends on behaviour and disclosure:

• Non-deliberate, unprompted disclosure: can be reduced to nil if you come forward promptly.
• Non-deliberate, prompted disclosure: a moderate percentage of the VAT.
• Deliberate or concealed failures: much higher percentages.

The clear lesson is that disclosing the error yourself, before HMRC contacts you, is far cheaper than being caught.

How to handle a missed registration

• Work out your true effective date of registration using the rolling 12-month figures.
• Register straight away and tell HMRC the failure was non-deliberate, if that is the case.
• Reconstruct your sales and purchases from the effective date to calculate output and input VAT.
• Where customers are VAT-registered businesses, issue VAT-only invoices so they can reclaim and you recover the VAT.
• Set money aside, as the backdated bill is often larger than expected.

Avoiding it next time

• Track your rolling 12-month turnover monthly, not just at year end.
• Watch for one-off large jobs that could push you over within 30 days.
• If you are close to GBP 90,000, decide in advance whether to register voluntarily or manage turnover.

To project when your turnover might cross the threshold and what VAT would cost, use the calchub.uk VAT calculator, and check the registration and penalty rules on gov.uk as soon as you think you may have registered late.