Glossary

UK tax terms explained in a sentence or two, with links to the tools that use them.

• HMRC fraud prevention headers — definition

  Fraud prevention headers are device and connection details software must send with every HMRC API call. What they contain and why you may be asked for consent.

• Quarterly update (MTD) — definition

  A quarterly update is the summary of income and expenses sent to HMRC every three months under MTD for Income Tax.

• Balancing payment — definition

  The balancing payment is the difference between your Self Assessment bill and the payments on account already made, due 31 January.

• VAT registration number (VRN) — definition

  A VAT registration number identifies a VAT-registered business. Format, where it appears, and how to check one.

• Personal Tax Account — definition

  Your Personal Tax Account is HMRC's online dashboard for tax code, NI record, PAYE income and Self Assessment. What you can see and do there.

• Government Gateway ID — definition

  A Government Gateway user ID is the 12-digit login for HMRC online services. How it differs from a UTR and how to recover it.

• Self Assessment — definition

  Self Assessment is the system for reporting income HMRC does not tax at source. Who files, the SA100 return, and the 31 January deadline.

• Making Tax Digital (MTD) — definition

  Making Tax Digital is HMRC's programme requiring digital records and API-based submissions for VAT and, from April 2026, Income Tax Self Assessment.